Gas diffusion electrode substrate and fuel cell

Abstract

Provided is a gas diffusion electrode substrate having excellent moisture retention and water drainage properties in a fuel cell, and having good power generation performance at a low current density and a high current density. A gas diffusion electrode substrate having a microporous layer on at least one surface of a conductive porous substrate, the gas diffusion electrode substrate having a filler containing an organic polymer in the microporous layer, the carbonization yield of the filler after heating at 1000 DEG C for 10 minutes being 55% or more, and the average particle diameter of the filler being 5-60 [mu] m, the filler is contained in an amount of 10-45% by mass per 100% by mass of the microporous layer, and the arithmetic average roughness Sa of the surface of the microporous layer is 5-20 [mu] m.

Description

Technical Field

[0001] The present invention relates to a fuel cell, in particular to a gas diffusion electrode substrate used in a solid polymer fuel cell and a fuel cell containing the gas diffusion electrode substrate. Background Art

[0002] A solid polymer fuel cell, which generates an electromotive force through electrochemical reactions at both electrodes by supplying a fuel gas containing hydrogen to the anode and an oxidizing gas containing oxygen to the cathode, is generally constructed by sequentially 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. The gas diffusion electrode substrate requires high gas diffusivity for diffusing the gas supplied from the diaphragm to the catalyst layer, high drainage for discharging water generated by the electrochemical reaction to the diaphragm, and high conductivity for extracting the generated current. Therefore, a gas diffusion electrode substrate using a carbon sheet composed of carbon fibers or the like as a substrate and having a microporous layer formed on its surface is widely used.

[0003] However, such gas diffusion electrode substrates have the following problems: (1) When operating a solid polymer fuel cell in a low current density region, the electrolyte membrane dries out due to a low amount of generated water, resulting in a dry condition and reduced proton conductivity, which in turn reduces power generation performance. (2) When operating in a high current density region, on the contrary, a high amount of generated water results in a wet condition, and the gas diffusion electrode substrate is clogged with generated water, resulting in insufficient gas supply and reduced power generation performance. Therefore, the gas diffusion electrode substrate needs to have both high moisture retention in the low current density region and high water drainage in the high current density region. To solve this problem, a method has been adopted to form a microporous layer on the surface of the gas diffusion electrode substrate and to incorporate particles into the microporous layer to improve moisture retention and water drainage.

[0004] For example, a gas diffusion electrode substrate including spacer particles in a microporous layer has been proposed (Patent Document 1).

[0005] Furthermore, a gas diffusion electrode substrate in which a microporous layer contains carbon powder has been proposed (Patent Document 2).

[0006] Furthermore, a gas diffusion electrode substrate containing a hydrophilic additive in a microporous layer has been proposed (Patent Document 3).

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Laid-Open No. 2006-331717

[0010] Patent Document 2: Japanese Patent Application Laid-Open No. 2016-195060

[0011] Patent Document 3: International Publication No. 2014 / 014463 Summary of the Invention

[0012] Problems to be solved by the invention

[0013] However, the technology described in Patent Document 1 improves gas diffusivity through spacer particles, achieving high drainage, but does not emphasize moisture retention. Similarly, the technology described in Patent Document 2 improves adhesion to the catalyst layer and drainage by creating surface irregularities with carbon powder, but also lacks moisture retention. Furthermore, the technology described in Patent Document 3 improves moisture retention and drainage through the use of hydrophilic additives, but the use of inorganic substances such as metal oxides and carbon black as hydrophilic additives results in insufficient results.

[0014] Therefore, in view of the above-mentioned background of the prior art, an object of the present invention is to provide a gas diffusion electrode substrate having both moisture retention and drainage properties, which have been difficult to achieve conventionally, and having excellent power generation performance at low and high current densities.

[0015] Means of solving problems

[0016] The embodiments of the present invention are as follows.

[0017] (1) A gas diffusion electrode substrate comprising a conductive porous substrate having a microporous layer on at least one surface thereof, wherein the microporous layer comprises a filler containing an organic polymer, wherein the carbonization yield of the filler after heating at 1000°C for 10 minutes is 55% or more, the average particle size of the filler is 5 to 60 μm, the filler is contained in 100% by mass of the microporous layer in an amount of 10 to 45% by mass, and the arithmetic mean roughness Sa of the surface of the microporous layer is 5 to 20 μm.

[0018] (2) The gas diffusion electrode substrate according to (1), wherein the F / C ratio of the surface of the microporous layer is 0.2 to 0.6.

[0019] (3) The gas diffusion electrode substrate according to (1) or (2), wherein the O / C ratio on the surface of the microporous layer is 0.1 or less.

[0020] (4) In the gas diffusion electrode substrate according to any one of (1) to (3), the average particle size of the filler is larger than the thickness of the microporous layer.

[0021] (5) In the gas diffusion electrode substrate according to any one of (1) to (4), the average particle size of the filler is 10 to 30 μm.

[0022] (6) In the gas diffusion electrode substrate according to any one of (1) to (5), the organic polymer is at least one resin selected from phenolic resin, acrylic resin, ester resin, and ether resin.

[0023] (7) In the gas diffusion electrode substrate according to any one of (1) to (6), the organic polymer is a phenolic resin.

[0024] (8) In the gas diffusion electrode substrate according to any one of (1) to (7), the microporous layer has a thickness of 3 to 55 μm.

[0025] (9) The gas diffusion electrode substrate according to any one of (1) to (8), wherein the microporous layer has pores with an average diameter of 10 to 60 μm, and the area ratio of the pores formed in the entire cross section of the microporous layer is 10 to 50%.

[0026] (10) The gas diffusion electrode substrate according to any one of (1) to (9), wherein the conductive porous substrate is carbon paper.

[0027] (11) A fuel cell comprising the gas diffusion electrode substrate according to any one of (1) to (10).

[0028] Effects of the Invention

[0029] According to the present invention, it is possible to obtain a gas diffusion electrode substrate that achieves both moisture retention and drainage, which have been difficult to achieve conventionally, and that has excellent power generation performance at both low and high current densities. DETAILED DESCRIPTION

[0030] The gas diffusion electrode substrate of the present invention comprises a conductive porous substrate having a microporous layer on at least one surface thereof. The microporous layer contains a filler containing an organic polymer having a carbonization yield of 55% or higher after heating at 1000°C for 10 minutes and an average particle size of 5 to 60 μm. The filler is present in an amount of 10 to 45% by mass relative to 100% by mass of the microporous layer, and the arithmetic mean roughness Sa of the surface of the microporous layer is 5 to 20 μm.

[0031] Hereinafter, the conductive porous substrate, the microporous layer, and the fuel cell constituting the gas diffusion electrode substrate of the present invention will be described in detail.

[0032] 〔Conductive porous substrate〕

[0033] As the conductive porous substrate in the present invention, a porous substrate containing carbon fibers or a porous metal body is generally used. Among these, porous substrates containing carbon fibers, such as carbon fiber fabrics, carbon fiber paper, carbon felt, and carbon paper, are preferably used in the present invention. "Carbon paper" herein refers to a sheet made by bonding carbon fiber paper with a binder such as a resin carbide. Carbon paper is particularly preferred due to its excellent corrosion resistance and ability to absorb dimensional changes in the thickness direction of the electrolyte membrane, i.e., its "springiness."

[0034] Preferred carbon fibers for the conductive porous substrate include polyacrylonitrile (PAN), pitch, and rayon. PAN and pitch-based carbon fibers are preferred due to their excellent mechanical strength. Natural fibers such as rayon, acrylic fibers, and cellulose fibers, as well as synthetic fibers, may also be mixed.

[0035] The average diameter of the carbon fiber single fibers is preferably 3 to 20 μm. When the average diameter is 3 μm or greater, the pore size of the conductive porous substrate increases, improving gas diffusivity and water drainage, thereby enhancing the power generation performance of the fuel cell. On the other hand, when the average diameter is 20 μm or less, water vapor diffusivity decreases, which can suppress performance degradation due to drying of the electrolyte membrane or catalyst layer. In other words, moisture retention is improved. When the average diameter of the carbon fiber single fibers is 5 to 10 μm, these effects are enhanced, making it more preferable.

[0036] When using a carbon fiber papermaking body or carbon paper as the conductive porous substrate, the average length of the carbon fiber single fibers is preferably 3 to 20 mm. An average length of 3 mm or greater provides excellent mechanical strength, electrical conductivity, and thermal conductivity of the conductive porous substrate. On the other hand, an average length of 20 mm or less provides excellent dispersion of the carbon fibers during papermaking, resulting in a homogeneous conductive porous substrate. An average length of 5 to 15 mm is more preferred, as these effects are enhanced.

[0037] The mass per unit area (ie, basis weight) of the conductive porous substrate is preferably 20 to 50 g / m 2 If the basis weight is 20g / m 2 On the other hand, if the weight is 50 g / m 2 If the weight of the conductive porous substrate is 30 to 40 g / m 2 , these effects are enhanced, so it is more preferred.

[0038] The basis weight of the conductive porous substrate can be adjusted by controlling the amount of carbon fibers, resin carbide, and the like, which are constituent materials of the conductive porous substrate.

[0039] As the conductive porous substrate, it is preferable to use one in which a hydrophobic resin is attached to the interior through a hydrophobic treatment. As the hydrophobic resin, fluororesins having a fluoroalkyl chain are preferred. Examples of such fluororesins include PTFE (polytetrafluoroethylene), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), ETFE (tetrafluoroethylene-ethylene copolymer), PVDF (polyvinylidene fluoride), and PVF (polyvinyl fluoride). PTFE and FEP, which exhibit high hydrophobicity, are preferred.

[0040] The amount of the hydrophobic resin is not particularly limited, but is preferably 0.1 to 20% by mass relative to 100% by mass of the entire conductive porous substrate. Within this range, the hydrophobicity can be fully exhibited, while also preventing the hydrophobic resin from clogging pores that serve as gas diffusion paths and suppressing increases in electrical resistance.

[0041] In polymer electrolyte fuel cells, the gas diffusion electrode substrate requires high gas diffusivity for diffusing the gas supplied from the diaphragm toward the catalyst, as well as high water drainage for discharging water generated during the electrochemical reaction toward the diaphragm. Therefore, the conductive porous substrate preferably has a pore diameter peak between 10 and 100 μm. The pore diameter and its distribution can be determined by measuring the pore size distribution using a mercury porosimeter. To determine the pore diameter of the conductive porous substrate, the conductive porous substrate alone can be measured, or the gas diffusion electrode substrate after the microporous layer has been formed can be measured. When measuring the gas diffusion electrode substrate, a scanning electron microscope (SEM) is used to observe a cross-section parallel to the thickness of the gas diffusion electrode substrate to confirm the structure of each layer. The diameter of the pores in the conductive porous substrate is then roughly determined from the SEM image. Next, the pore diameter of the conductive porous substrate is determined by comparing the multiple pore diameter peaks obtained by mercury porosimetry with the approximate values ​​measured using the SEM image.

[0042] In the present invention, the porosity of the conductive porous substrate is preferably 80-95%. A porosity of 80% or higher improves gas diffusion and power generation performance. On the other hand, a porosity of 95% or lower improves the mechanical strength and electrical conductivity of the conductive porous substrate. A porosity of 85-90% is more preferred, as these effects are enhanced. The porosity of the conductive porous substrate can be measured using a hydrometer, for example.

[0043] The thickness of the conductive porous substrate of the present invention is preferably 90 to 180 μm. Here, the "thickness of the conductive porous substrate" refers to the thickness when the two surfaces are clamped at a pressure of 0.15 MPa. When the thickness is 90 μm or more, the mechanical strength can be maintained and the handling in the manufacturing process is easy. In addition, the springiness becomes higher, the gas diffusion electrode substrate can absorb the dimensional changes caused by the expansion and contraction of the electrolyte membrane during the use of the fuel cell, and the gas diffusivity in the in-plane direction is good, so the power generation performance is improved. On the other hand, when the thickness of the conductive porous substrate is 180 μm or less, the gas diffusivity in the thickness direction is improved, and the conductive path in the thickness direction becomes shorter, the conductivity becomes good, and thus the power generation performance is improved. When the thickness of the conductive porous substrate is 110 to 150 μm, these effects are improved, so it is more preferred.

[0044] 〔Microporous layer〕

[0045] Next, the microporous layer is described. The gas diffusion electrode substrate of the present invention has a microporous layer on at least one side of the conductive porous substrate, but preferably has a microporous layer only on one side of the conductive porous substrate. As the functions of the microporous layer, water management such as moisturizing the electrolyte membrane or catalyst layer and discharging generated water, reducing the interface resistance between the catalyst layer and the gas diffusion electrode substrate, and suppressing damage to the electrolyte membrane caused by carbon fibers protruding from the conductive porous substrate can be listed. In order to improve moisture retention and drainage, the present invention has a filler containing an organic polymer. Furthermore, it is preferably a layer containing carbon particles and a hydrophobic resin.

[0046] The filler component of the present invention is not particularly limited as long as it contains an organic polymer. For example, filler components containing phenolic resins, acrylic resins, ester resins, ether resins, fluororesins, styrene resins, polyurethane resins, and melamine resins can be used. The carbonization yield after heating at 1000°C for 10 minutes must be 55% or higher. A carbonization yield of 55% or higher after heating at 1000°C for 10 minutes means that water-affinity sites such as hydroxyl groups and ester bonds of the organic polymer remain appropriately, thereby improving moisture retention and water drainage. Furthermore, as carbonization proceeds appropriately, electrical conductivity improves, thereby enhancing the power generation performance of the fuel cell.

[0047] As the organic polymer, at least one resin selected from phenolic resins, acrylic resins, ester resins, and ether resins is preferably used, with phenolic resins being particularly preferred. The carbonization yield can be measured using a TGA apparatus such as the EXTRATGA6200 manufactured by SII. Specifically, under a nitrogen atmosphere, the temperature is increased from 50°C to 1000°C at a rate of 10°C / min and then maintained at 1000°C for 10 minutes. The mass after holding at 1000°C is then divided by the initial mass, and the resultant mass is multiplied by 100, which is the carbonization yield.

[0048] Furthermore, the carbon crystallite diameter Lc(002), which indicates the degree of graphitization of the organic polymer-containing filler of the present invention, is preferably 15 angstroms or less. A crystallite diameter of 15 angstroms or less allows for sufficient organic polymer presence, improving moisture retention and water repellency. Furthermore, the crystallite diameter of carbon black is typically greater than 20 angstroms, and that of graphite is typically greater than 100 angstroms.

[0049] The average particle size of the filler of the present invention is 5 to 60 μm. An average particle size of 5 μm or greater improves moisture retention and drainage, and enhances power generation performance at both low and high current densities. On the other hand, an average particle size of 60 μm or less enhances the conductivity of the microporous layer, improving power generation performance. An average particle size of 10 to 30 μm is more preferred, as these effects are enhanced.

[0050] The method for measuring the above-mentioned average particle size from the gas diffusion electrode substrate is described. First, an ion milling device is used to randomly prepare 10 cross-sectional observation samples obtained by cutting the gas diffusion electrode substrate parallel to the thickness direction. At this time, there is no special limitation on the cutting position of the gas diffusion electrode substrate, and the size of the cross-sectional observation sample is set to 5 mm (width of the cross-sectional cut portion) × 12 mm. Next, a scanning electron microscope is used to obtain an image of the cross section of the microporous layer at any position of the sample magnified 1000 times. The image analysis software "ImageJ" is used to measure the area of ​​each filler present in the microporous layer in the image, and the equivalent circle diameter is calculated by substituting it into the following formula, and the average value of the equivalent circle diameter obtained in the image is calculated. The above operation is performed on the images of the 10 samples in the same way, and the arithmetic average of the whole is taken as the average particle size of the filler.

[0051]

[0052] The filler of the present invention is preferably spherical because the conductivity of the microporous layer is improved. Furthermore, the surface of the microporous layer has large irregularities, which facilitates the retention of water vapor and contributes to improved moisture retention.

[0053] In the present invention, the term "spherical filler" means that the filler has an aspect ratio (the ratio of the major diameter to the minor diameter) in the range of 1.0 to 1.3. Here, the major diameter is the longest line segment connecting two points within the filler, and the minor diameter is the longest line segment perpendicular to the major diameter.

[0054] The method for measuring the aspect ratio is described below. Using an ion milling device, 10 cross-sectional observation samples were randomly prepared by cutting the gas diffusion electrode substrate parallel to the thickness direction. At this time, there is no particular limitation on the cutting position of the gas diffusion electrode substrate, and the size of the cross-sectional observation sample was set to 5 mm (width of the cross-sectional cut portion) × 12 mm. Next, using a scanning electron microscope, the cross section of the microporous layer at any position of the sample was magnified 300 times to obtain an image. Using the image analysis software "ImageJ", the major and minor axes of each filler present in the microporous layer in the image were measured, the aspect ratio was calculated, and the average value was calculated. The same operation was performed on the images of the 10 samples, and the arithmetic average of the entire image was taken as the aspect ratio of the filler.

[0055] The filler content of the present invention is 10-45% by mass, preferably 20-30% by mass, based on 100% by mass of the microporous layer. A filler content of 10% by mass or greater provides sufficient moisture retention and drainage. Furthermore, a filler content of 45% by mass or less provides enhanced mechanical strength, electrical conductivity, and thermal conductivity of the microporous layer, resulting in excellent power generation performance. A more preferred filler content is 20-40% by mass.

[0056] The following describes a method for measuring the filler content in a gas diffusion electrode substrate. First, a portion of the microporous layer is scraped from the gas diffusion electrode substrate and its mass is measured. Next, the scraped microporous layer is heated in air at 500°C for one hour. The filler is then separated from the remaining mixture of carbon particles and filler using, for example, a membrane filter. The filler content is then measured and its mass is calculated as mass %.

[0057] In addition, the average particle size of the filler of the present invention is preferably greater than the thickness of the microporous layer. In this way, the surface roughness of the microporous layer is improved, water vapor is easily retained, and it helps to improve moisture retention. In addition, when the microporous layer is formed on the conductive porous substrate, sometimes a part of the microporous layer will be immersed in the conductive porous substrate. The "thickness of the microporous layer" mentioned here refers to the thickness of the part not immersed in the conductive porous substrate, which can be calculated by subtracting the thickness of the conductive porous substrate from the thickness of the gas diffusion electrode substrate. The thickness of the conductive porous substrate can be measured before the microporous layer is formed, or after the microporous layer is removed from the gas diffusion electrode substrate by heating it at 500°C in air for 1 hour and wiping it off.

[0058] Next, the carbon particles preferably contained in the microporous layer will be described. Specifically, carbon black, carbon nanofibers, carbon nanotubes, graphene, etc. can be used as carbon particles. Among them, inexpensive carbon black is preferably used.

[0059] The specific surface area of ​​the carbon particles is preferably 20 to 40 m 2 / g. The method for measuring the specific surface area is not particularly limited and can be obtained by, for example, nitrogen adsorption. The so-called "nitrogen adsorption method" is a method in which degassed carbon particles are sealed together with nitrogen in a container cooled to liquid nitrogen temperature, the amount of nitrogen adsorbed on the surface of the carbon particles at equilibrium is measured, and the specific surface area is calculated based on this value. When the specific surface area of ​​the carbon particles is 20m 2 When the specific surface area of ​​the carbon particles is 40 m 2 When the carbon content is less than 1%, the oxidative corrosion reaction of carbon is suppressed, thereby improving the durability of the fuel cell.

[0060] Furthermore, fibrous carbon particles such as carbon nanofibers and carbon nanotubes form conductive paths inside the microporous layer, thereby having the effect of reducing the electrical resistance of the microporous layer.

[0061] As the hydrophobic resin preferably contained in the above-mentioned microporous layer, a fluororesin having a fluoroalkyl chain is preferably used in view of chemical stability and hydrophobicity. Similar to the fluororesins preferably used when the conductive porous substrate is subjected to a hydrophobic treatment, examples thereof include PTFE (polytetrafluoroethylene), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), and ETFE (tetrafluoroethylene-ethylene copolymer).

[0062] Fluororesins are generally insoluble in water, organic solvents, and the like. Therefore, when preparing the coating solution for forming the microporous layer (described later), it is preferable to use a dispersion of a hydrophobic resin processed into fine particles. Examples of such dispersions include POLYFLON (registered trademark) D-210C and ND-110 (both manufactured by Daikin Industries, Ltd.), 120-JRB, and 31-JR (both manufactured by Chemours-Mitsui Fluoroproducts Co., Ltd.).

[0063] As the hydrophobic resin, polysiloxane having a siloxane bond can also be used.

[0064] In addition to a filler having a carbonization yield of 55% or higher after heating at 1000°C for 10 minutes and an average particle size of 5 to 60 μm and a hydrophobic resin, a thermosetting resin may also be contained. Examples of the thermosetting resin include phenolic resin, epoxy resin, acrylate resin, and furan resin.

[0065] In order to improve moisture retention and drainage, pores may be formed in the microporous layer. A method of forming pores by incorporating a pore-forming agent that burns out at high temperatures into the microporous layer and then sintering and burning it out is preferred.

[0066] The microporous layer of the present invention preferably has pores with an average diameter of 10 to 60 μm. Pore diameters of 10 μm or greater improve drainage and power generation performance at high current densities. On the other hand, pore diameters of 60 μm or less improve moisture retention and power generation performance at low current densities. Pore diameters of 30 to 50 μm are more preferred, as these effects are enhanced.

[0067] In the present invention, the "average diameter of the pores" refers to the average value of the equivalent circular diameters of the pores. As a measurement method, the gas diffusion electrode substrate is cut parallel to the thickness direction using an ion milling device. The cross section of the obtained sample is magnified to 1000 times using a scanning electron microscope to obtain an image. The image analysis software "ImageJ" is used to measure the area of ​​each pore present in the microporous layer in the image, and the equivalent circular diameter is calculated by substituting it into the following formula. The average value of the equivalent circular diameters of 1 μm or more among the obtained equivalent circular diameters is used as the average diameter. 10 samples are cut out, and the arithmetic average of the average diameters of each of the 10 samples is used as the average diameter of the microporous layer.

[0068]

[0069] The area ratio of pores formed in the entire cross-section of the microporous layer (hereinafter referred to as "cross-sectional porosity") is preferably 10 to 50%. A cross-sectional porosity of 10% or greater improves drainage and power generation performance at high current densities. On the other hand, a cross-sectional porosity of 50% or less improves moisture retention and power generation performance at low current densities. A cross-sectional porosity of 15 to 30% is more preferred, as these effects are enhanced.

[0070] The "cross-sectional porosity" mentioned above refers to the area ratio of pores within the entire cross-section of a sample obtained by cutting the microporous layer parallel to the thickness. The measurement method involves obtaining a 1000x magnified image of the cross-section using a scanning electron microscope. Using the image analysis software "ImageJ," the area of ​​pores with an equivalent circle diameter of 1 μm or greater is measured. The cross-sectional porosity is calculated as the ratio of the pore area to the total cross-sectional area of ​​the microporous layer. Ten samples are cut out, and the arithmetic average of the cross-sectional porosities of each of the ten samples is used as the cross-sectional porosity of the microporous layer.

[0071] Pores can be formed by mixing a pore former in a coating liquid for forming a microporous layer described later, applying the coating liquid on a conductive porous substrate, and then sintering the liquid to burn out the pore former.

[0072] The material for the pore-forming agent is not particularly limited, as long as it burns or shrinks under the sintering conditions of the gas diffusion electrode substrate, forming pores within the microporous layer. Examples include acrylic resins, styrene resins, starch, polylactic acid resins, sublimable low-molecular-weight materials, and hollow microspheres. "Sublimable low-molecular-weight materials" are generally low-molecular-weight organic powders with a molecular weight of 1000 or less that sublimate and burn at sintering temperatures. Examples of sublimable low-molecular-weight materials include anthracene, pentacene, and phenanthrene. Hollow microspheres are hollow particles that expand significantly upon heating, forming pores around them. Ultimately, the resin portion thermally decomposes or shrinks, leaving only the pores. Various materials are commercially available. Examples include "Matsumoto Microsphere (registered trademark)" (manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd.) and "Expancel (registered trademark)" (manufactured by Japan Fillite Co., Ltd.).

[0073] Regarding the amount of pore-forming agent in the microporous layer-forming coating liquid, when the coating liquid contains carbon microparticles, the amount of carbon microparticles per 100 parts by mass is preferably 10 to 200 parts by mass, and more preferably 30 to 100 parts by mass. A pore-forming agent amount of 10 parts by mass or greater ensures sufficient pores and good drainage. A pore-forming agent amount of 200 parts by mass or less provides excellent mechanical strength, electrical conductivity, and thermal conductivity of the microporous layer, resulting in good power generation performance.

[0074] In addition, microparticles of iridium oxide, ruthenium oxide, titanium oxide, etc. may be contained to promote water electrolysis under the reverse potential state when hydrogen is deficient. Furthermore, microparticles of cerium oxide, manganese oxide, etc. may be contained to deactivate hydroxide radicals generated at the anode electrode.

[0075] The basis weight (weight per unit area) of the microporous layer of the present invention is preferably 5 to 35 g / m 2If the microporous layer has a basis weight of 5 g / m 2 The above mentioned coating will cover the carbon fibers protruding from the surface of the conductive porous substrate, thereby preventing damage to the electrolyte membrane. In addition, the contact resistance between the gas diffusion electrode substrate and the catalyst layer can be reduced, and the electrolyte membrane can be prevented from drying out. In addition, when the basis weight of the microporous layer is 35 g / m 2 The drainage is good when the microporous layer has a basis weight of 10 to 25 g / m 2 These effects are enhanced when , so it is more preferred.

[0076] The thickness of the microporous layer is preferably 3 to 55 μm. A thickness of 3 μm or greater covers carbon fibers and other materials protruding from the surface of the conductive porous substrate, thereby preventing damage to the electrolyte membrane and improving moisture retention. On the other hand, a thickness of 55 μm or less improves the conductivity of the gas diffusion electrode substrate and further enhances water drainage. A thickness of 5 to 40 μm is more preferred, as these effects are enhanced.

[0077] The thickness of the microporous layer is measured by placing the conductive porous substrate on a smooth surface and measuring the thickness of the conductive porous substrate under an applied pressure of 0.15 MPa. The thickness of the gas diffusion electrode substrate, on which the microporous layer is formed, is similarly measured. The thickness of the microporous layer is then calculated by subtracting the thickness of the conductive porous substrate from the thickness of the gas diffusion electrode substrate. When measuring the thickness of the gas diffusion electrode substrate, the microporous layer can be removed by heating it in air at 500°C for 1 hour and then wiping it off. The thickness of the conductive porous substrate is then removed, and the thickness difference between before and after removal of the microporous layer is calculated.

[0078] The arithmetic mean roughness Sa of the surface of the microporous layer of the present invention is 5 to 20 μm. When Sa is 5 μm or greater, the surface has large surface roughness, water vapor easily accumulates, moisture retention is improved, and power generation performance at low current density is improved. On the other hand, when Sa is 20 μm or less, the adhesion between the microporous layer and the catalyst layer is improved, and the mechanical properties and durability of the microporous layer itself are improved. When Sa is 6 to 15 μm, these effects are enhanced and are therefore more preferred. The arithmetic mean roughness (Sa) can be determined by measuring Sa at any four locations on the microporous layer side surface of a 30 mm × 30 mm gas diffusion electrode substrate sample over an area of ​​8.4 mm × 6.0 mm using a laser microscope or the like, and calculating the average value.

[0079] The fluorine atom / carbon atom ratio (F / C ratio) on the surface of the microporous layer of the present invention is preferably 0.2 to 0.6. An F / C ratio of 0.2 or greater improves surface hydrophobicity and water repellency. On the other hand, an F / C ratio of 0.6 or less improves moisture retention.

[0080] The oxygen atom / carbon atom ratio (O / C ratio) on the surface of the microporous layer of the present invention is preferably 0.1 or less. If the O / C ratio exceeds 0.1, the electrical conductivity may decrease, and the power generation performance may decrease.

[0081] The F / C and O / C ratios can be measured by performing elemental analysis at five random locations on the surface of the microporous layer of the gas diffusion electrode substrate using an X-ray photoelectron spectroscopy (XPS) system. The concentrations of fluorine (F), oxygen (O), and carbon (C) are then quantified, and the F / C and O / C ratios are calculated. The average values ​​of the values ​​at the five locations are then used for measurement.

[0082] The microporous layer can be formed by applying the above-mentioned microporous layer-forming coating liquid containing the filler and carbon fine particles to at least one surface of the conductive porous substrate.

[0083] The coating liquid may contain a dispersion medium such as water or an organic solvent, and may contain a dispersion aid such as a surfactant. Water is preferably used as the dispersion medium, and a nonionic surfactant is preferably used as the dispersion aid.

[0084] The coating liquid can be applied to the conductive porous substrate using various commercially available coating devices. Examples of coating methods include screen printing, rotary screen printing, spraying, gravure printing, die coating, rod coating, and blade coating. These coating methods are merely illustrative and are not necessarily limiting.

[0085] After applying the coating liquid to the conductive porous substrate, the coating liquid is preferably dried at a temperature of 80-180°C. Specifically, the coated material is preferably placed in a dryer set at a temperature of 80-180°C and dried for 2-30 minutes. The drying air volume can be appropriately adjusted, but rapid drying may sometimes induce microcracks on the surface. After drying, the coated material is placed in a muffle furnace, a calcining furnace, or a high-temperature dryer and sintered for 5-20 minutes, preferably at a temperature of 300-380°C. This melts the hydrophobic resin, which acts as a binder between the carbon particles, thereby forming a microporous layer.

[0086] Gas diffusion electrode substrate

[0087] The thickness of the gas diffusion electrode substrate of the present invention is preferably 130 to 190 μm. Here, the thickness of the gas diffusion electrode substrate is the thickness when the two surfaces are clamped at a pressure of 0.15 MPa. When the thickness of the gas diffusion electrode substrate is 130 μm or greater, mechanical strength can be maintained, and handling during the manufacturing process is easy. On the other hand, when the thickness of the gas diffusion electrode substrate is 190 μm or less, gas diffusivity is improved and electrical resistance is reduced, thereby improving the power generation performance of the fuel cell. The thickness of the gas diffusion electrode substrate can be adjusted by appropriately adjusting the thickness of the conductive porous substrate and the microporous layer.

[0088] [Membrane Electrode Assembly]

[0089] In the present invention, a membrane electrode assembly can be formed by bonding the gas diffusion electrode substrate described above to at least one surface of a solid polymer electrolyte membrane having a catalyst layer on both surfaces. Preferred solid polymer electrolyte membranes are those with high proton conductivity, high oxidation resistance, and low gas crossover. Examples include membranes composed of fluorine-based polymers or hydrocarbon-based polymers. Furthermore, the catalyst layer is preferably a mixture of catalyst-supported carbon particles supported on carbon particles by catalyst fine particles of a noble metal such as platinum, palladium, ruthenium, iridium, or rhodium, or their oxides, and a proton-conducting polymer.

[0090] When a gas diffusion electrode substrate is joined to a solid polymer electrolyte membrane having a catalyst layer, by arranging the microporous layer side of the gas diffusion electrode substrate on the catalyst layer side, effects such as moisture retention of the electrolyte membrane and the catalyst layer, discharge of generated water, reduction of the interface resistance between the catalyst layer and the gas diffusion electrode substrate, and suppression of damage to the electrolyte membrane caused by carbon fibers protruding from the conductive porous substrate are exhibited.

[0091] Fuel Cell

[0092] The fuel cell of the present invention comprises the gas diffusion electrode substrate of the present invention. Specifically, the fuel cell of the present invention comprises separators on both sides of the membrane electrode assembly. Specifically, the fuel cell is constructed by placing separators on both sides of the membrane electrode assembly. Typically, a polymer electrolyte fuel cell is constructed by stacking multiple cells (fuel cell units) sandwiched between separators via gaskets on both sides of such a membrane electrode assembly. For example, 200 to 500 fuel cell cells can be prepared and connected in series to generate a high voltage of 40 to 200 kV. This fuel cell stack can be used as a power source for fuel cell vehicles, etc.

[0093] Example

[0094] Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to the following description.

[0095] [Raw Materials] Fillers

[0096] ・Phenolic resin particles "BellPearl (registered trademark)" C800 (manufactured by Air Water BellPearl Co., Ltd., spherical, average particle size (catalog value): 15 μm, aspect ratio: 1.0, carbonization yield after heating at 1000°C for 10 minutes: 95%, crystallite diameter Lc (002): 11 angstroms

[0097] ・Phenolic resin particles "BellPearl (registered trademark)" R700 (manufactured by Air Water BellPearl Co., Ltd., spherical, average particle size (catalog value): 15μm, aspect ratio: 1.0, carbonization yield after heating at 1000°C for 10 minutes: 60%

[0098] BellPearl (registered trademark) C2000SR phenolic resin particles (manufactured by Air Water BellPearl Co., Ltd., spherical, average particle size (catalog value): 8 μm, aspect ratio: 1.0, carbonization yield after heating at 1000°C for 10 minutes: 99%)

[0099] ・LPS (registered trademark) 50C phenolic resin particles (manufactured by REIGNITE Co., Ltd., spherical, average particle size (catalog value): 50 μm, aspect ratio: 1.0, carbonization yield after heating at 1000°C for 10 minutes: 56%)

[0100] ・Phenolic resin particles "LPS (registered trademark)" 50A (manufactured by REIGNITE Co., Ltd., spherical, average particle size: 50 μm, aspect ratio: 1.0, carbonization yield after heating at 1000°C for 10 minutes: 52%

[0101] ・Phenolic resin particles "BellPearl (registered trademark)" R100 (manufactured by Air Water BellPearl Co., Ltd., spherical, average particle size (catalog value): 1.5μm, aspect ratio: 1.0, carbonization yield after heating at 1000°C for 10 minutes: 60%

[0102] ・Phenolic resin particles "LPS (registered trademark)" 100C (manufactured by REIGNITE Co., Ltd., spherical, average particle size (catalog value): 100 μm, aspect ratio: 1.0, carbonization yield after heating at 1000°C for 10 minutes: 57%)

[0103] Fibrous conductive potassium titanate "DENTALL (registered trademark)" WK-200B (manufactured by Otsuka Chemical Co., Ltd., fibrous form, fiber length: 15 μm, aspect ratio: 50, carbonization yield after heating at 1000°C for 10 minutes: 95%).

[0104] <Measurement of basis weight of microporous layer>

[0105] The mass [g] of the conductive porous substrate was measured using a precision scale in a 10 cm square. Next, the mass [g] of the gas diffusion electrode substrate on which the microporous layer was formed was measured in the same 10 cm square. The mass of the conductive porous substrate was subtracted from the mass of the gas diffusion electrode substrate and the result was divided by the sample area (0.01 m2). 2 ), the obtained value is taken as the basis weight of the microporous layer [g / m 2 ].

[0106] <Measurement of thickness of microporous layer>

[0107] Place the conductive porous substrate on a smooth surface and measure the height difference between the presence and absence of the test object (conductive porous substrate) under an applied pressure of 0.15 MPa. Samples are taken at 10 different locations, and the average of the height difference values ​​is used as the thickness of the conductive porous substrate. Next, measure the thickness of the gas diffusion electrode substrate with a microporous layer formed thereon in the same manner. Subtract the thickness of the conductive porous substrate from the thickness of the gas diffusion electrode substrate to obtain the thickness (μm) of the microporous layer.

[0108] <Determination of Carbonization Yield of Filler>

[0109] The carbonization yield was measured using a TGA apparatus (EXTRA TGA6200 manufactured by SII). Under a nitrogen atmosphere, the temperature was increased from 50°C to 1000°C at a rate of 10°C / min and held at 1000°C for 10 minutes. The mass after the 1000°C hold was divided by the initial mass, and the resultant value was multiplied by 100. The carbonization yield (%) was calculated.

[0110] <Calculation of filler content>

[0111] The filler content can be calculated by the following formula.

[0112] Filler content [mass %] = mass of filler contained in the microporous layer / mass of the microporous layer.

[0113] Here, we describe a method for measuring the filler content (mass %) of the microporous layer from a gas diffusion electrode substrate. First, a portion of the microporous layer is scraped from the gas diffusion electrode substrate, and its mass (mass A) is measured. Next, the scraped microporous layer is heated at 500°C in air for one hour. The remaining mixture of carbon particles and filler is mixed with pure water. The filler is then separated using a membrane filter with a pore size of 0.45 μm (Advantec Toyo Co., Ltd.). The mass of the membrane filter after drying is measured (mass B), and the result is calculated as mass B / mass A × 100.

[0114] <Measurement of Surface Arithmetic Mean Roughness Sa>

[0115] The arithmetic mean roughness (Sa) of the microporous layer side of the gas diffusion electrode substrate was measured using a VK-X100 laser microscope (manufactured by KEYENCE Corporation) over an area of ​​8.4 mm x 6.0 mm. Sa was measured at four random locations on a 30 mm x 30 mm sample, and the average value was calculated.

[0116] <Measurement of surface F / C ratio>

[0117] Using an X-ray photoelectron spectroscopy (XPS) MODEL 5400 (manufactured by ULVAC-PHI Co., Ltd.), elemental analysis was performed at five random locations on the surface of the microporous layer of the gas diffusion electrode substrate. The fluorine (F) and carbon (C) elemental concentrations [%] were quantified, and the F / C ratio was calculated, with the average value at the five locations calculated.

[0118] Determination of surface O / C ratio

[0119] Using an X-ray photoelectron spectroscopy (XPS) MODEL 5400 (manufactured by ULVAC-PHI Co., Ltd.), elemental analysis was performed at five random locations on the surface of the microporous layer of the gas diffusion electrode substrate. The oxygen (O) and carbon (C) elemental concentrations [%] were quantified, the O / C ratio was calculated, and the average value of the five values ​​was calculated.

[0120] <Measurement of average pore diameter>

[0121] First, using an ion milling device IM4000 (manufactured by Hitachi High-Tech Corporation), 10 cross-sectional observation samples were randomly prepared by cutting the gas diffusion electrode substrate parallel to the thickness direction. The cutting position of the gas diffusion electrode substrate was not particularly limited, and the size of the cross-sectional observation sample was set to 5 mm (width of the cut section) × 12 mm. Next, using a scanning electron microscope SU8010 (manufactured by Hitachi High-Tech Corporation), an image of the microporous layer at any position of the sample was obtained at 1000x magnification. The area of ​​each pore in the image was measured using the image analysis software "ImageJ" and the equivalent circle diameter was calculated using the following formula. The average of the equivalent circle diameters obtained was calculated for those with an equivalent circle diameter of 1 μm or more. The same operation was repeated for the images of the 10 samples, and the arithmetic mean of the total was taken as the average pore diameter.

[0122]

[0123] <Measurement of cross-sectional porosity>

[0124] As described in the "Measurement of Average Pore Diameter" section above, ten cross-sectional observation samples were prepared by cutting the gas diffusion electrode substrate parallel to the thickness direction. Images of the microporous layer at arbitrary locations were obtained at 1000x magnification. The area of ​​pores with an equivalent circle diameter of 1 μm or greater, as indicated in the "Measurement of Average Pore Diameter," was measured using the image analysis software "ImageJ." The ratio of the pore area to the total area of ​​the microporous layer was then calculated. The same procedure was repeated for the images of the ten samples, and the arithmetic average of the total was taken as the cross-sectional porosity (%).

[0125] <Evaluation of Power Generation Characteristics>

[0126] 1.00 g of platinum-supported carbon (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., platinum supporting amount: 50% by mass), 1.00 g of purified water, 8.00 g of "Nafion (registered trademark)" solution (5.0% by mass of "Nafion (registered trademark)" manufactured by Sigma Aldrich Co., Ltd.), and 18.00 g of isopropyl alcohol (manufactured by Nacalai Tesque Co., Ltd.) were added in this order to prepare a catalyst solution.

[0127] Next, the catalyst solution was sprayed onto a 50 mm × 50 mm cut PTFE tape "NAFLON (registered trademark)" "TOMBO (registered trademark)" No. 9001 (manufactured by Nichias Corporation) and dried at room temperature to produce a platinum-loaded film with a platinum content of 0.3 mg / cm 2A PTFE sheet with a catalyst layer was prepared. Next, a solid polymer electrolyte membrane (10 μm thickness) was prepared using a 10% by mass dispersion of "Nafion (registered trademark)" (manufactured by Sigma-Aldrich) and cut into 80 mm x 80 mm pieces. The resulting solid polymer electrolyte membrane was sandwiched between two PTFE sheets with catalyst layers and pressed at 130°C for 5 minutes using a flatbed press while applying 5 MPa to transfer the catalyst layer onto the solid polymer electrolyte membrane. After pressing, the PTFE sheets were peeled off, producing a solid polymer electrolyte membrane with a catalyst layer.

[0128] Next, a solid polymer electrolyte membrane with a catalyst layer was sandwiched between two gas diffusion electrode substrates cut into 50 mm x 50 mm pieces. The membrane electrode assembly was then pressed at 130°C for 5 minutes while applying 3 MPa of pressure using a flat plate press. The gas diffusion electrode substrates were positioned so that the surface with the microporous layer was in contact with the catalyst layer.

[0129] The resulting membrane electrode assembly was assembled into a fuel cell for fuel cell evaluation, and the voltage was measured while varying the current density. Furthermore, evaluation was performed while supplying unpressurized hydrogen to the anode side and unpressurized air to the cathode side.

[0130] The unit temperature was set to 65°C, and the humidity in the unit was 80% by humidifying the supplied hydrogen and air at 60°C. The utilization rates of hydrogen and oxygen in the air were set to 70% and 40%, respectively. The current density was measured at 0.5 A / cm 2 or 2.0A / cm 2 The output voltage is used as an indicator of dry performance (humidity retention) and wet performance (drainage).

[0131] <Method for producing a conductive porous substrate>

[0132] Toray Industries, Inc.'s polyacrylonitrile carbon fiber "Torayca (registered trademark)" T300 (average fiber diameter: 7 μm) was cut into 6 mm lengths, dispersed in water, and continuously made into paper. A 10% by mass aqueous solution of polyvinyl alcohol was then sprayed on the paper and dried to obtain a paper with a basis weight of 30 g / m 2 The amount of polyvinyl alcohol attached to 100 parts by mass of the paper sheet was 15 parts by mass.

[0133] Next, a resin composition solution was prepared by mixing flaky graphite (average particle size: 5 μm), a phenolic resin (a mixture of a resol-type phenolic resin and a novolac-type phenolic resin at a mass ratio of 1:1), and methanol at a mass ratio of 5:10:85. The resin composition solution was then continuously applied to the paper sheet by spray coating, such that the total amount of phenolic resin and flaky graphite was 130 parts by mass per 100 parts by mass of the carbon fibers in the conductive porous substrate, and dried at 100°C for 5 minutes.

[0134] Next, a press-molding machine was used to heat and compress the paper sheet, which had been coated with the resin composition, at 180°C for 5 minutes while sandwiched between upper and lower hot plates. Release paper was placed between the paper sheet and the hot plates to prevent adhesion between the hot plates and the paper sheet substrate. Furthermore, spacers were placed around the edges of the upper and lower hot plates to adjust the thickness of the conductive porous substrate after heat and compression. The sheet was then heated to 2400°C in a heating furnace under a nitrogen atmosphere for carbonization.

[0135] Furthermore, a hydrophobic resin dispersion prepared by mixing 5 parts by mass of FEP resin ("NEOFLON (registered trademark)" FEP DISPERSION ND-110 (manufactured by Daikin Industries, Ltd.) and 95 parts by mass of ion-exchanged water) was spray-coated and dried at 100°C for 5 minutes to obtain a film having a thickness of 150 μm and a basis weight of 40 g / m at 0.15 MPa. 2 conductive porous substrate.

[0136] (Example 1)

[0137] The coating solution for forming the microporous layer was prepared by mixing "BellPearl (registered trademark)" C800 phenolic resin particles as a filler, "DENKA BLACK (registered trademark)" powder (manufactured by DENKA Corporation) as carbon fine particles, fluororesin PTFE as a hydrophobic resin, "TRITON (registered trademark)" X-100 (manufactured by Nacalai Tesque Co., Ltd.) as a dispersant, and purified water as a dispersion medium in the proportions shown in Table 1. The PTFE source was "POLYFLON (registered trademark)" D-210C (manufactured by Daikin Industries, Ltd.), a dispersion of PTFE particles in water. A planetary mixer was used to disperse the raw materials and achieve a uniform coating solution composition.

[0138] The conductive porous substrate prepared according to the above-mentioned <Method for Producing a Conductive Porous Substrate> was coated with the above-mentioned coating liquid for forming a microporous layer using a die coater, dried at 120°C for 10 minutes, and then heated at 380°C for 10 minutes to promote adhesion between the hydrophobic resin and the carbon particles and decompose and remove the dispersant, thereby producing a gas diffusion electrode substrate. Here, the basis weight of the microporous layer after heating was 12 g / m 2 The coating amount was adjusted in this manner. The thickness of the resulting gas diffusion electrode substrate was 160 μm. Furthermore, evaluations were performed as described above for <Calculation of Filler Content>, <Measurement of Surface F / C Ratio>, and <Measurement of Surface O / C Ratio>. The results are shown in Table 1.

[0139] Next, the power generation performance was evaluated as described in the above-mentioned <Evaluation of Power Generation Characteristics>. As shown in Table 1, the power generation performance was good.

[0140] (Example 2)

[0141] A gas diffusion electrode substrate was prepared in the same manner as in Example 1 except that phenolic resin particles "BellPearl (registered trademark)" R700 were used as the filler, and various evaluations were performed.

[0142] (Example 3)

[0143] A gas diffusion electrode substrate was prepared in the same manner as in Example 1 except that phenolic resin particles "BellPearl (registered trademark)" C2000SR were used as the filler and the basis weight and thickness were set as shown in Table 1, and various evaluations were performed.

[0144] (Example 4)

[0145] A gas diffusion electrode substrate was prepared in the same manner as in Example 1 except that phenolic resin particles “LPS (registered trademark)” 50C were used as the filler, and various evaluations were performed.

[0146] (Examples 5 and 6)

[0147] A gas diffusion electrode substrate was prepared in the same manner as in Example 1 except that the composition of the coating liquid for forming the microporous layer was as shown in Table 1, and various evaluations were performed.

[0148] (Example 7)

[0149] A gas diffusion electrode substrate was prepared in the same manner as in Example 1 except that phenolic resin particles "LPS (registered trademark)" 50C were used as the filler and the basis weight and thickness were set as shown in Table 1, and various evaluations were performed.

[0150] (Example 8)

[0151] A gas diffusion electrode substrate was prepared in the same manner as in Example 1 except that phenolic resin particles "BellPearl (registered trademark)" C2000SR were used as the filler, and various evaluations were performed.

[0152] (Example 9)

[0153] A gas diffusion electrode substrate was prepared in the same manner as in Example 1 except that the basis weight and thickness were set as shown in Table 2, and various evaluations were performed.

[0154] (Examples 10 and 11)

[0155] A gas diffusion electrode substrate was prepared in the same manner as in Example 1 except that the composition, basis weight, and thickness of the coating solution for forming the microporous layer were as shown in Table 2, and various evaluations were performed.

[0156] (Example 12)

[0157] A gas diffusion electrode substrate was prepared in the same manner as in Example 1, except that the composition, basis weight, and thickness of the coating solution for forming the microporous layer were as shown in Table 2. Various evaluations were performed. PMMA beads "TECHPOLYMER (registered trademark)" MBX-40 (manufactured by Sekisui Chemicals Co., Ltd., average particle size: 40 μm) were used as a pore-forming agent. The evaluation results for the aforementioned "Measurement of Average Pore Diameter" and "Measurement of Cross-Sectional Porosity" are shown in Table 2.

[0158] (Comparative Example 1)

[0159] A gas diffusion electrode substrate was prepared in the same manner as in Example 1, except that phenolic resin particles "LPS (registered trademark)" 50A were used as the filler, and various evaluations were performed. The carbonization yield of the filler in this gas diffusion electrode substrate was as low as 52%, resulting in reduced conductivity and decreased power generation characteristics at both low and high current densities.

[0160] (Comparative Example 2)

[0161] A gas diffusion electrode substrate was prepared in the same manner as in Example 1, except that "BellPearl (registered trademark)" R100 phenolic resin particles were used as the filler, and the basis weight and thickness were set to the values ​​shown in Table 3. Various evaluations were performed. The average particle size of the filler in this gas diffusion electrode substrate was small, at 1.4 μm, resulting in reduced moisture retention and water drainage, and consequently, reduced power generation characteristics at both low and high current densities.

[0162] (Comparative Example 3)

[0163] A gas diffusion electrode substrate was prepared in the same manner as in Example 1, except that phenolic resin particles "LPS (registered trademark)" 100C were used as filler, and various evaluations were performed. The average particle size of the filler in this gas diffusion electrode substrate was large, at 75 μm, resulting in reduced conductivity and decreased power generation characteristics at both low and high current densities.

[0164] (Comparative Example 4)

[0165] A gas diffusion electrode substrate was prepared in the same manner as in Example 1, except that fibrous conductive potassium titanate "DENTALL (registered trademark)" WK-200B (manufactured by Otsuka Chemical Co., Ltd., fiber length: 15 μm, carbonization yield: 95% after heating at 1000°C for 10 minutes) was used as a filler. The average particle size of this gas diffusion electrode substrate filler was 0.6 μm, resulting in reduced conductivity and decreased power generation characteristics at both low and high current densities.

[0166] (Comparative Examples 5 and 6)

[0167] A gas diffusion electrode substrate was prepared in the same manner as in Example 1, except that the composition of the coating solution for forming the microporous layer was as shown in Table 3. Various evaluations were performed. The gas diffusion electrode substrate of Comparative Example 5 had a filler content as low as 4% by mass, resulting in reduced moisture retention and water drainage, and decreased power generation characteristics on both the low and high current density sides. The gas diffusion electrode substrate of Comparative Example 6 had a filler content as high as 48% by mass, resulting in reduced electrical conductivity and decreased power generation characteristics on both the low and high current density sides.

[0168] (Comparative Example 7)

[0169] A gas diffusion electrode substrate was prepared in the same manner as in Example 1, except that no filler was added and the composition of the coating solution for forming the microporous layer was as shown in Table 3. Various evaluations were performed. Since this gas diffusion electrode substrate did not contain a filler, its moisture retention and water drainage properties were insufficient, resulting in reduced power generation characteristics at both low and high current densities.

[0170]

[0171]

[0172]

[0173] Industrial availability

[0174] The gas diffusion electrode substrate of the present invention has excellent moisture retention and water drainage properties, and a fuel cell using the gas diffusion electrode substrate has good power generation performance at both low and high current densities, and is therefore useful.

Claims

1. A gas diffusion electrode substrate comprising a conductive porous substrate having a microporous layer on at least one surface thereof, wherein the microporous layer comprises a filler containing an organic polymer, wherein the carbonization yield of the filler after heating at 1000° C. for 10 minutes is 55% or more, the average particle size of the filler is 5 to 60 μm, the filler is contained in an amount of 10 to 45% by mass per 100% by mass of the microporous layer, and the arithmetic mean roughness Sa of the surface of the microporous layer is 5 to 20 μm. 2 . The gas diffusion electrode substrate according to claim 1 , wherein the surface F / C ratio of the microporous layer is 0.2 to 0.

6. 3 . The gas diffusion electrode substrate according to claim 1 , wherein the O / C ratio on the surface of the microporous layer is 0.1 or less. 4 . The gas diffusion electrode substrate according to claim 1 , wherein the average particle size of the filler is larger than the thickness of the microporous layer. 5 . The gas diffusion electrode substrate according to claim 1 , wherein the average particle size of the filler is 10 to 30 μm. 6 . The gas diffusion electrode substrate according to claim 1 , wherein the organic polymer is at least one resin selected from the group consisting of phenolic resins, acrylic resins, ester resins, and ether resins. 7 . The gas diffusion electrode substrate according to claim 1 , wherein the organic polymer is a phenolic resin. 8 . The gas diffusion electrode substrate according to claim 1 , wherein the microporous layer has a thickness of 3 to 55 μm. 9 . The gas diffusion electrode substrate according to claim 1 , wherein the microporous layer has pores with an average diameter of 10 to 60 μm, and the area ratio of the pores formed in the entire cross section of the microporous layer is 10 to 50%.

10. The gas diffusion electrode substrate according to claim 1 or 2, wherein the conductive porous substrate is carbon paper.

11. A fuel cell comprising the gas diffusion electrode substrate according to claim 1 or 2.

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