Gas diffusion electrode substrate, method for manufacturing the same, and solid polymer fuel cell

Abstract

The microporous layer of the present invention can provide a fuel cell with high productivity, high power generation performance, and high durability. The present invention is a gas diffusion electrode substrate having a microporous layer on one side of a conductive porous substrate. The conductive porous substrate includes carbon fiber and resin carbide and has a density in the range of 0.25 to 0.39 g / cm 3 , a pore mode diameter in the range of 30 to 50 μm. The microporous layer includes carbonaceous powder and fluororesin, has a surface roughness of 2.0 to 6.0 μm, a porosity of 50 to 95%, and a pore mode diameter of 0.050 to 0.100 μm.

Description

Technical Field

[0001] The present invention relates to a gas diffusion electrode substrate used in a fuel cell, and particularly to a gas diffusion electrode substrate suitable for a solid polymer fuel cell used as a power source for a fuel cell vehicle or the like in a fuel cell. Background Art

[0002] The solid polymer fuel cell has high energy efficiency and the emission is only water, so it is expected that the solid polymer fuel cell will be popularized as a clean energy.

[0003] The basic structure of the solid polymer fuel cell is: a polymer electrolyte membrane, catalyst layers formed on both sides of the polymer electrolyte membrane, a gas diffusion electrode substrate formed outside the catalyst layer, and two separators sandwiching them.

[0004] A fuel cell is a system that extracts the energy generated when hydrogen and oxygen react to form water in the form of electric energy. Therefore, when the electrical load increases, that is, when the current drawn from the battery to the outside increases, a large amount of water (water vapor) is generated. This water vapor condenses at low temperatures and turns into water droplets, which block the pores of the gas diffusion electrode substrate, reducing the supply amount of gas (oxygen or hydrogen) to the catalyst layer. Then, when all the pores are finally blocked, power generation stops (this phenomenon is called flooding).

[0005] As the gas diffusion electrode substrate, a conductive porous substrate such as a carbon felt, carbon paper, and carbon cloth formed of carbon fiber is specifically used. However, since the mesh of the fiber is coarse, large water droplets are generated when water vapor condenses, and flooding is likely to occur. Therefore, a microporous layer (also called a microporous layer) containing conductive fine particles such as carbonaceous powder is sometimes provided on the conductive porous substrate.

[0006] Regarding this microporous layer, it is generally formed by drying and sintering an ink (hereinafter referred to as MPL ink) obtained by dispersing carbonaceous powder, fluororesin particles as its binder, and a surfactant in water. Here, since the melting point of the fluororesin is much higher than the drying temperature of the above MPL ink, there is a situation where the carbonaceous powder moves and aggregates significantly during drying, generating cracks called cracks, and even if the fluororesin is melted and moved by sintering, it cannot be repaired.

[0007] The cracks already formed in the microporous layer are likely to become the bases for water vapor condensation, so flooding is likely to occur and the performance is likely to decrease. In addition, since the electrolyte membrane swells and shrinks according to the operating conditions, the cracks are enlarged and / or the electrolyte membrane is damaged, resulting in a decrease in durability. In particular, in the case of a process of forming a catalyst layer by coating a catalyst coating liquid on the microporous layer, the catalyst coating liquid cannot be uniformly coated.

[0008] In Patent Document 1, a technique for forming a gas diffusion electrode substrate by changing the density of a conductive porous substrate is disclosed.

[0009] In Patent Document 2, the following technique is disclosed: a conductive porous substrate is subjected to a hydrophobic treatment, and then heat-treated at a high temperature of 300 °C or higher to improve the hydrophobicity of the conductive porous substrate, and then a microporous layer is formed.

[0010] In Patent Document 3, a technique for reducing the surface roughness by making the microporous layer have a double-layer structure is disclosed.

[0011] Prior art documents

[0012] Patent documents

[0013] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2011-195374

[0014] Patent Document 2: Japanese Unexamined Patent Application Publication No. 2011-171182

[0015] Patent Document 3: Japanese Unexamined Patent Application Publication No. 2006-310201 Summary of the invention

[0016] Problems to be solved by the invention

[0017] Regarding the technique described in Patent Document 1, although a technique for improving gas diffusibility and power generation performance by making the conductive porous substrate have a low density is disclosed, since pulp carbide is contained in the conductive porous substrate, the median pore diameter is small, and the improvement in power generation performance is limited. In addition, there is a problem that impurities from the pulp reduce the durability of the fuel cell.

[0018] Regarding the technique described in Patent Document 2, although a technique for improving the hydrophobicity of a conductive porous substrate by subjecting it to a hydrophobic treatment and then heat-treating it at a high temperature of 300 °C or higher and then coating the above-mentioned MPL ink is disclosed, since the penetration of the above-mentioned MPL ink into the conductive porous substrate is excessively inhibited, there is the following problem: the MPL ink is repelled and the surface roughness becomes large, the adhesion at the interface between the microporous layer and the conductive porous substrate is weak, and peeling easily occurs at the interface between the microporous layer and the conductive porous substrate. In addition, heat treatment at a high temperature is required before forming the microporous layer, so the manufacturing cost becomes high.

[0019] Regarding the technique described in Patent Document 3, the surface roughness can be reduced by making the microporous layer have a double-layer structure. In the present invention, making the microporous layer have a double-layer structure is not excluded, but since the above-mentioned MPL ink needs to be coated twice, the manufacturing cost becomes high.

[0020] Therefore, an object of the present invention is to provide a gas diffusion electrode substrate with high productivity, which improves power generation performance and durability when used in a fuel cell.

[0021] Means for Solving the Problems

[0022] To solve the above problems, the present invention provides a gas diffusion electrode substrate having a microporous layer on one side of a conductive porous substrate.

[0023] The above-mentioned conductive porous substrate includes carbon fiber and resin carbide, and has a density in the range of 0.25 to 0.39 g / cm 3 and a pore mode diameter in the range of 30 to 50 μm.

[0024] The above-mentioned microporous layer includes carbonaceous powder and fluororesin, and has a surface roughness of 2.0 to 6.0 μm, a porosity of 50 to 95%, and a pore mode diameter of 0.050 to 0.100 μm.

[0025] In addition, a method for manufacturing the gas diffusion electrode substrate of the present invention is provided, in which a fluororesin and a hydrophobic processing additive different from the fluororesin are simultaneously imparted to the conductive porous substrate, and then MPL ink is coated. The MPL ink is obtained by dispersing carbonaceous powder, fluororesin particles, and a surfactant in water.

[0026] Effects of the Invention

[0027] By using the gas diffusion electrode substrate of the present invention, a fuel cell with high productivity, high power generation performance, and high durability can be obtained. Detailed Embodiments

[0028] The gas diffusion electrode substrate of the present invention has a microporous layer on at least one side of a conductive porous substrate.

[0029] As the conductive porous substrate, specifically, for example, it is preferable to use a porous substrate containing carbon fiber such as carbon fiber fabric, carbon fiber paper, carbon fiber non-woven fabric, carbon felt, carbon paper, carbon cloth, etc., a metal porous substrate such as foamed sintered metal, metal mesh, and metal plate mesh. Among them, from the aspect of excellent corrosion resistance, it is necessary to contain carbon fiber, and it is preferable to use a porous substrate such as carbon felt, carbon paper, and carbon cloth containing carbon fiber. In addition, from the aspect of excellent characteristics of absorbing dimensional changes in the thickness direction of the electrolyte membrane, that is, "elasticity", it is necessary to contain resin carbide, and it is preferable to use a substrate containing resin carbide obtained by bonding a carbon fiber paper with resin carbide, that is, carbon paper.

[0030] The density of the conductive porous substrate used in the gas diffusion electrode substrate of the present invention is 0.25 to 0.39 g / cm 3When the density of the above-mentioned conductive porous substrate is 0.25 g / cm 3 or more, the carbon fibers are easily bonded by the resin carbide, and the conductivity and strength of the conductive porous substrate are improved, so it is preferred. In addition, when the density of the above-mentioned conductive porous substrate is 0.25 g / cm 3 or more, it is not easy to cause local short circuits inside the fuel cell due to the carbon fibers piercing the electrolyte membrane, so it is preferred. Considering these aspects, the density of the above-mentioned conductive porous substrate is preferably 0.26 g / cm 3 or more, more preferably 0.28 g / cm 3 or more. Further preferably 0.30 g / cm 3 or more. In addition, when the density of the above-mentioned conductive porous substrate is 0.39 g / cm 3 or less, the gas diffusibility of the above-mentioned conductive porous substrate is improved, and the power generation performance is improved, so it is preferred. Considering these aspects, the density of the above-mentioned conductive porous substrate is preferably 0.37 g / cm 3 or less, more preferably 0.35 g / cm 3 or less.

[0031] In the present invention, the density of the substrate is a value calculated based on the mass measured with a square having a side length of 10 cm and the thickness obtained using a micrometer under a state where a surface pressure of 0.15 MPa is applied. The thickness is the average value obtained by measuring 10 or more points within the range of a square having a side length of 10 cm.

[0032] The pore mode diameter of the conductive porous substrate used in the gas diffusion electrode substrate of the present invention is 30 to 50 μm. When the pore mode diameter of the above-mentioned conductive porous substrate is 30 μm or more, liquid water is easily removed from the conductive porous substrate, and the power generation performance at low temperatures is improved. Considering these aspects, the pore mode diameter of the above-mentioned conductive porous substrate is more preferably 35 μm or more. In addition, when the pore mode diameter of the above-mentioned conductive porous substrate is 50 μm or less, the infiltration of MPL ink can be suppressed in the coating process of the microporous layer, and the surface quality of the microporous layer is improved. Considering these aspects, the pore mode diameter of the above-mentioned conductive porous substrate is more preferably 45 μm or less.

[0033] In the case of a substrate obtained by bonding a carbon fiber paper sheet such as carbon paper with a resin carbide, by increasing the ratio of the resin carbide to the carbon fibers, the pore mode diameter can be made smaller, or by reducing the density of the above-mentioned conductive porous substrate while fixing the ratio of the resin carbide to the carbon fibers, the pore mode diameter can be increased.

[0034] In the present invention, the so-called pore mode diameter refers to the pore diameter at the peak in the pore size distribution (a curve obtained by plotting the horizontal axis as the pore diameter and the vertical axis as the Log differential pore volume) that can be measured by the mercury intrusion method. Additionally, the Log differential pore volume refers to the value obtained by plotting the value obtained by dividing the differential pore volume dV by the differential value d(LogD) of the logarithmic process of the pore diameter with respect to the average pore diameter of each interval. The pore mode diameter of the conductive porous substrate used in the gas diffusion electrode substrate refers to the peak position above 1 μm in the pore size distribution, and the pore mode diameter of the microporous layer refers to the peak position below 1 μm in the pore size distribution.

[0035] Regarding the measurement of the pore mode diameter, a specimen piece can be cut out from the gas diffusion electrode substrate, accurately weighed, placed in a measurement unit, mercury can be injected under reduced pressure, and the measurement can be carried out under the following conditions.

[0036] · Measurement pressure range: 6 kPa (400 μm) to 414 MPa (30 nm)

[0037] · Measurement unit mode: The pressure increasing process within the above pressure range

[0038] · Unit volume: 5 cm 3

[0039] · Surface tension of mercury: 485 dyn / cm

[0040] · Contact angle of mercury: 130°

[0041] As the measurement device, Autopore 9520 manufactured by Shimadzu Corporation or its equivalent can be used.

[0042] In the present invention, from the viewpoint of improving gas diffusibility, it is preferable to reduce the thickness of the conductive porous substrate such as carbon paper. That is, the thickness of the conductive porous substrate such as carbon paper is preferably 220 μm or less, more preferably 150 μm or less, particularly preferably 120 μm or less. However, if it is too thin, the mechanical strength becomes weak. Therefore, in order to facilitate the operation in the manufacturing process, it is generally preferably 70 μm or more.

[0043] Regarding the conductive porous substrate in the present invention, it is also a preferred method to apply hydrophobic treatment for the purpose of improving drainage. Fluororesin exhibits hydrophobicity when heat-treated at a high temperature of 300 °C or higher. Therefore, the conductive porous substrate used in the present invention preferably contains a hydrophobic resin such as fluororesin. Examples of the hydrophobic resin contained in the conductive porous substrate, that is, the fluororesin contained in the conductive porous substrate, include PTFE (polytetrafluoroethylene) (e.g., "Teflon" (registered trademark)), FEP (tetrafluoroethylene hexafluoropropylene copolymer), PFA (perfluoroalkoxy fluororesin), ETFE (ethylene tetrafluoroethylene copolymer), PVDF (polyvinylidene fluoride), PVF (polyvinyl fluoride), etc. PTFE or FEP, which preferably exhibits strong hydrophobicity, is more preferred. The amount of the hydrophobic resin is not particularly limited, and it is appropriate to be 0.1% by mass or more and 20% by mass or less based on 100% by mass of the entire conductive porous substrate. When it is less than 0.1% by mass, the hydrophobicity may not be sufficiently exhibited. When it exceeds 20% by mass, the pores that serve as the gas diffusion path or the drainage path may be blocked, or the resistance may increase.

[0044] In addition, regarding the conductive porous substrate in the present invention, it is preferred that, in the process of hydrophobic treatment, a hydrophobic treatment additive different from the above-mentioned fluororesin is imparted simultaneously with the above-mentioned fluororesin. As the hydrophobic treatment additive different from the above-mentioned fluororesin, an organosilicon-based hydrophobic treatment additive, a paraffin-based hydrophobic treatment additive, a polymer compound having a side chain formed by a perfluoroalkyl group or a hydrocarbon group on the main chain of an acrylate polymer (hydrocarbon-based hydrophobic treatment additive), etc. are preferred. A fluorine-free hydrophobic treatment additive that does not emit perfluorooctanoic acid, which is known to cause an environmental burden, is more preferred. In addition, as the hydrocarbon-based hydrophobic treatment additive, the number of carbon atoms of the side-chain hydrocarbon group is preferably 12 or more and 24 or less, and a straight-chain alkyl group is more preferred.

[0045] In addition, the hydrophobic treatment additive different from the above-mentioned fluororesin will undergo thermal decomposition and leave hydrophilic residues when heat-treated at a high temperature of 300 °C or higher. Therefore, when the hydrophobic treatment additive before heat treatment is set to 100%, its mass retention rate is preferably 50% or less, and more preferably 20% or less. In order to achieve a low weight retention rate when heat-treated at a high temperature of 300 °C or higher, the hydrophobic treatment additive different from the above-mentioned fluororesin preferably does not contain a block isocyanate-based crosslinking agent or a melamine resin.

[0046] When it is a hydrocarbon-based hydrophobic processing additive, examples include "NEOSEED (trade name)" manufactured by Nippon Kayaku Co., Ltd., "Paragium ECO (trade name)" manufactured by Ohara Paragium Chemical Co., Ltd., "RACGUARD NOF (trade name)" manufactured by Rakuto Kasei Kogyo Co., Ltd., etc. When it is a silicone-based hydrophobic processing additive, examples include "DRYPON 600E (trade name)" manufactured by Nippon Kayaku Co., Ltd., "Poron (trade name)" manufactured by Shin-Etsu Silicone Co., Ltd., etc. When it is a wax-based hydrophobic processing additive, examples include "TH-44 (trade name)" manufactured by Nippon Kayaku Co., Ltd., "Neolax (trade name)" manufactured by Takamatsu Oil & Fat Co., Ltd., etc.

[0047] As described above, in the case of using a silicone-based hydrophobic processing additive or the like, the surface of the conductive porous substrate on the side opposite to the surface having the microporous layer of the gas diffusion electrode substrate in the present invention may contain silicon, and the silicon / carbon element ratio at this time is preferably 0.020 or more. When the above-mentioned silicon / carbon element ratio is 0.020 or more, the penetration of the MPL ink into the conductive porous substrate is suppressed in the coating process of the microporous layer, the cracks in the microporous layer are reduced, and the surface roughness becomes smaller. In addition, by suppressing the penetration of the MPL ink into the conductive porous substrate in the coating process of the microporous layer, the porosity of the conductive porous substrate becomes higher, the gas diffusibility and drainage performance become higher, the overflow can be further suppressed, and the power generation performance is improved. Considering these aspects, the above-mentioned silicon / carbon element ratio is more preferably 0.025 or more, and further preferably 0.030 or more.

[0048] In addition, when the above-mentioned silicon / carbon element ratio is 0.050 or less, the hydrophobicity of the conductive porous substrate does not become too high, and the adhesion at the interface between the microporous layer and the conductive porous substrate becomes stronger, which is preferable. In addition, when the above-mentioned silicon / carbon element ratio is 0.050 or less, the hydrophilicity of the surface of the gas diffusion electrode substrate is reduced, so the drainage performance of the gas diffusion electrode substrate becomes higher, the overflow can be further suppressed, and the power generation performance is improved. Considering these aspects, the above-mentioned silicon / carbon element ratio is more preferably 0.045 or less, and further preferably 0.040 or less.

[0049] The gas diffusion electrode substrate having the above-mentioned silicon / carbon element ratio of 0.020 to 0.050 can be obtained by the following method: in the hydrophobic processing step of the conductive porous substrate described later, a silicone-based hydrophobic processing additive having a silicon atom in its molecular structure is imparted simultaneously with the above-mentioned fluororesin. By increasing the amount of the hydrophobic processing additive having a silicon atom in its molecular structure attached, the above-mentioned silicon / carbon element ratio can be increased.

[0050] Here, the above-mentioned silicon / carbon element ratio can be obtained as follows: For the surface of the conductive porous substrate on the side opposite to the surface with the microporous layer of the gas diffusion electrode substrate, scanning electron microscope (SEM)-EDX measurement is performed under the conditions of an acceleration voltage of 20 kV and a magnification of 2000 times, and the average value of more than 10 measurements is obtained.

[0051] In the present invention, the oxygen / carbon element ratio on the surface of the conductive porous substrate on the side opposite to the surface with the microporous layer of the gas diffusion electrode substrate is preferably 0.005 or more. When the above-mentioned oxygen / carbon element ratio is 0.005 or more, it is shown that the infiltration of MPL ink into the conductive porous substrate is suppressed in the coating process of the microporous layer, the cracks in the microporous layer are reduced, and the surface roughness becomes smaller. In addition, by suppressing the infiltration of MPL ink into the conductive porous substrate in the coating process of the microporous layer, the porosity of the conductive porous substrate becomes higher, the gas diffusivity and drainage performance become higher, the overflow can be further suppressed, and the power generation performance is improved. Considering these aspects, the above-mentioned oxygen / carbon element ratio is more preferably 0.006 or more, and further preferably 0.007 or more.

[0052] In addition, when the above-mentioned oxygen / carbon element ratio is 0.015 or less, the hydrophobicity of the conductive porous substrate does not become too high, and the adhesion at the interface between the microporous layer and the conductive porous substrate becomes stronger, which is preferable. In addition, when the above-mentioned oxygen / carbon element ratio is 0.015 or less, the hydrophilicity of the surface of the gas diffusion electrode substrate is reduced, so the drainage performance of the gas diffusion electrode substrate becomes higher, the overflow can be further suppressed, and the power generation performance is improved. Considering these aspects, the above-mentioned oxygen / carbon element ratio is more preferably 0.013 or less, and further preferably 0.011 or less.

[0053] The gas diffusion electrode substrate with the above-mentioned oxygen / carbon element ratio of 0.005 to 0.015 can be obtained by the following method: In the hydrophobic treatment process of the conductive porous substrate described below, a hydrophobic treatment additive having an oxygen atom in the molecular structure is imparted simultaneously with the above-mentioned fluororesin. By increasing the adhesion amount of the hydrophobic treatment additive having an oxygen atom in the molecular structure, the above-mentioned oxygen / carbon element ratio can be increased.

[0054] Here, the above-mentioned oxygen / carbon element ratio can be obtained as follows: For the surface of the conductive porous substrate on the side opposite to the surface with the microporous layer of the gas diffusion electrode substrate, scanning electron microscope (SEM)-EDX measurement is performed under the conditions of an acceleration voltage of 20 kV and a magnification of 2000 times, and the average value of more than 10 measurements is obtained.

[0055] In the present invention, when the pore mode diameter of the gas diffusion electrode substrate is 30 to 50 μm, per 1 cm 2 the cumulative pore volume is preferably in the range of 1.5 to 4.0 μL / cm2 within the range. The above cumulative pore volume is 1.5 μL / cm 2 When it is 1.5 μL / cm or more, the pores of the conductive porous substrate become more numerous, the gas diffusivity and drainage property become higher, overflows can be further suppressed, and the power generation performance is improved. Considering these aspects, the above cumulative pore volume is more preferably 1.7 μL / cm 2 or more, and further preferably 2.0 μL / cm 2 or more. In addition, when the above cumulative pore volume is 4.0 μL / cm 2 or less, the thickness of the conductive porous substrate is likely to be within an appropriate range, the gas diffusivity and drainage property become higher, overflows can be further suppressed, and the power generation performance is improved. Considering these aspects, the above cumulative pore volume is more preferably 3.5 μL / cm 2 or less, and further preferably 3.0 μL / cm 2 or less.

[0056] The above cumulative pore volume of 1.5 to 4.0 μL / cm 2 of the gas diffusion electrode substrate can be obtained by controlling the density and thickness of the conductive porous substrate and the penetration of MPL ink in the coating process of the microporous layer. For example, by making the density of the conductive porous substrate smaller, or the thickness larger, or the penetration of MPL ink in the coating process of the microporous layer smaller, a gas diffusion electrode substrate with a large above cumulative pore volume can be obtained.

[0057] Here, the above cumulative pore volume is obtained as follows: dividing the pore volume obtained for each pore diameter by mercury intrusion porosimetry by the unit area weight of the gas diffusion electrode substrate, and accumulating within the range of pore diameters of 30 to 50 μm. Here, the unit area weight of the gas diffusion electrode substrate is obtained by dividing the mass of the gas diffusion electrode substrate weighed using an electronic balance by the area of the gas diffusion electrode substrate. For the measurement of the above cumulative pore volume, three specimen pieces of about 12 mm × 20 mm square can be cut out from the gas diffusion electrode substrate, accurately weighed, and then placed in the measurement unit in a non-overlapping manner, and mercury is injected under reduced pressure, and the measurement is carried out under the following conditions.

[0058] · Measurement pressure range: 6 kPa (400 μm) to 414 MPa (30 nm)

[0059] · Measurement unit mode: the pressure increase process in the above pressure range

[0060] · Unit volume: 5 cm 3

[0061] · Surface tension of mercury: 485 dyn / cm

[0062] · Contact angle of mercury: 130°

[0063] As the measuring device, Autopore 9520 manufactured by Shimadzu Corporation or its equivalent can be used.

[0064] In the present invention, the coverage rate (permeability) based on carbonaceous powder in the surface of the conductive porous substrate on the side opposite to the side having the microporous layer of the gas diffusion electrode substrate is preferably less than 10%. When the above-mentioned permeability is less than 10%, it is shown that the infiltration of MPL ink into the conductive porous substrate is suppressed in the coating process of the microporous layer, the cracks in the microporous layer are reduced, and the surface roughness becomes smaller. In addition, by suppressing the infiltration of MPL ink into the conductive porous substrate in the coating process of the microporous layer, the porosity of the conductive porous substrate becomes higher, the gas diffusibility and drainage performance become higher, the overflow can be further suppressed, and the power generation performance is improved. Considering from these aspects, the above-mentioned permeability is more preferably less than 8%, and further preferably less than 6%. The smaller the above-mentioned permeability, the more preferable, but usually it is 0.1% or more. The gas diffusion electrode substrate with a permeability less than 10% can be obtained by the following methods: in the manufacturing method described later, increasing the density of the conductive porous substrate; increasing the hydrophobicity of the conductive porous substrate to suppress the infiltration of MPL ink into the conductive porous substrate in the coating process of the microporous layer; or reducing the mode diameter of the pores of the conductive porous substrate; and so on.

[0065] Here, the above-mentioned permeability can be obtained, for example, according to the following steps. First, take a photograph of the surface of the conductive porous substrate on the side opposite to the side having the microporous layer of the gas diffusion electrode substrate at an observation magnification of 200 times. As the scanning electron microscope, S-5500 manufactured by Hitachi, Ltd. or its equivalent can be used. Randomly select different parts from the gas diffusion electrode substrate and take photographs until 10 images of the above-mentioned surface are obtained. Then, cut out the part covered with carbonaceous powder from the obtained images and perform binarization. There are various methods of binarization. In the case where the part covered with carbonaceous powder and the part not covered with carbonaceous powder can be clearly distinguished, a method of visual discrimination can be adopted. In the present invention, a method using image processing software or the like is preferably adopted. Here, as the image processing software, Adobe Photoshop (registered trademark) manufactured by Adobe System Inc. or JTrim can be used. Next, the processing method when using JTrim v1.53c will be described. It is preferable to perform normalization processing on each image, and then perform double grayscale conversion with a threshold value of 128 to obtain a binarized image. In each of the obtained binarized images, calculate the ratio (%) of the area of the part covered with carbonaceous powder to the photographed area, and find its average value as the above-mentioned permeability. When finding the ratio of the area using image processing software, it is preferable to calculate the number of pixels.

[0066] In the present invention, the in-plane gas diffusivity of the gas diffusion electrode substrate is preferably in the range of 40 to 80 cc / min. When the in-plane gas diffusivity is 40 cc / min or more, gas can be sufficiently diffused in the in-plane direction inside the fuel cell, so the power generation performance is improved. Considering these aspects, the in-plane gas diffusivity is more preferably 50 cc / min or more, and further preferably 60 cc / min or more. In addition, when the in-plane gas diffusivity is 80 cc / min or less, the gas discharged without being used inside the fuel cell is reduced, so it is preferred. Considering these aspects, the in-plane gas diffusivity is more preferably 75 cc / min or less, and further preferably 70 cc / min or less.

[0067] The gas diffusion electrode substrate with the in-plane gas diffusivity of 40 to 80 cc / min can be obtained by controlling the density and thickness of the gas diffusion electrode substrate and the penetration of MPL ink in the coating process of the microporous layer. Here, the gas diffusion electrode substrate with a large in-plane gas diffusivity can be obtained by making the density of the gas diffusion electrode substrate smaller, or making the thickness larger, or making the penetration of MPL ink in the coating process of the microporous layer smaller.

[0068] Here, the in-plane gas diffusivity can be obtained by flowing gas at a certain pressure through the cross-section (section in the thickness direction) of the gas diffusion electrode substrate and measuring its flow rate (cc / min). The measurement can be carried out in the following manner: nitrogen is used as the gas type, the measurement pressure is set to 5 kPa relative to the atmospheric pressure, the measurement area is 8 mm in length and 24 mm in width, and the gas flows through the substrate horizontally. As the measurement device, a water vapor gas water vapor permeation and diffusion evaluation device MVDP-200C manufactured by Seika Sangyo Co., Ltd. or its equivalent can be used.

[0069] <Microporous layer>

[0070] The microporous layer in the present invention contains carbonaceous powder and fluororesin, and the surface roughness of the microporous layer is 2.0 to 6.0 μm. The porosity of the microporous layer is 50 to 95%, and the pore mode diameter is 0.050 to 0.100 μm.

[0071] When the porosity of the microporous layer is 50% or more, the gas diffusivity and drainage performance become high, overflows can be further suppressed, and the power generation performance is improved, so it is preferred. Considering these aspects, the porosity of the above microporous layer is more preferably 60% or more, and further preferably 70% or more. In addition, when the porosity of the above microporous layer is 95% or less, the conductivity is improved, so it is preferred. Considering these aspects, the porosity of the above microporous layer is more preferably 90% or less, and further preferably 85% or less.

[0072] The above-mentioned microporous layer with a porosity of 50 to 95% can be obtained by the following method: in the manufacturing method described below, control the compounding amount of the carbonaceous powder relative to the fluororesin and other materials of the microporous layer and the type of the carbonaceous powder. Here, by increasing the compounding amount of the carbonaceous powder relative to the fluororesin and other materials, it is easy to obtain a microporous layer with a high porosity. By decreasing the compounding amount of the carbonaceous powder relative to the fluororesin and other materials, a microporous layer with a low porosity can be obtained.

[0073] Here, regarding the porosity of the microporous layer, for a cross-section observation sample prepared using an ion milling device, a microscope such as a scanning electron microscope is used to magnify it by more than 1000 times to take a photograph, measure the area of the void part, and obtain the ratio of the area of the void part to the observation area. As the scanning electron microscope, S-5500 manufactured by Hitachi, Ltd. or its equivalent can be used.

[0074] When the surface roughness of the microporous layer is 6.0 μm or less, the electrolyte membrane is not easily damaged, and the durability of the fuel cell can be improved. It should be noted that the "surface" in the surface roughness referred to here means the surface on the opposite side of the surface in contact with the conductive porous substrate. Considering these aspects of the gas diffusion electrode substrate, the surface roughness of the above-mentioned microporous layer is more preferably 5.5 μm or less, and further preferably 5.0 μm or less. The smaller the above surface roughness, the more preferable it is, and it is usually 2.0 μm or more. The above-mentioned microporous layer with a surface roughness of 2.0 to 6.0 μm can be obtained by the following method: in the manufacturing method described below, increase the density of the conductive porous substrate; increase the hydrophobicity of the conductive porous substrate, thereby suppressing the penetration of MPL ink in the coating process of the microporous layer; or decrease the mode diameter of the pores of the conductive porous substrate; decrease the permeability of the gas diffusion electrode substrate; and so on.

[0075] Here, the surface roughness of the microporous layer can be obtained using a non-contact roughness measuring machine. As the device, a shape measuring machine VR-3200 manufactured by KEYENCE Corporation can be used. It can be fixed to the device in a state where the microporous layer faces upward without floating or wrinkling, and measurement can be performed in a field of view of 48 mm 2 . Measurement is performed at any 10 locations on the surface of the microporous layer, and the average value of the arithmetic mean roughness Ra at these 10 locations is used as the surface roughness.

[0076] When the pore mode diameter of the microporous layer is 0.050 μm or more, the gas diffusibility of the microporous layer becomes high and the power generation performance of the gas diffusion electrode substrate becomes high, so it is preferable. Considering these aspects, the pore mode diameter of the microporous layer is more preferably 0.070 μm or more. When the pore mode diameter of the microporous layer is 0.100 μm or less, the microporous layer is not easily crushed and the short-circuit resistance is improved, so it is preferable. In addition, when the pore mode diameter of the microporous layer is 0.100 μm or less, it is not easily a condensation base point of water vapor, so overflow is not likely to occur. In addition, in the case of a process of forming a catalyst layer by coating a catalyst coating liquid on the microporous layer, the catalyst coating liquid is not easily infiltrated into the microporous layer and can be uniformly coated. Considering these aspects, the pore mode diameter of the microporous layer is more preferably 0.090 μm or less. The microporous layer with a pore mode diameter of 0.050 to 0.100 μm can be controlled by changing the primary particle diameter of the carbonaceous powder contained in the microporous layer. By increasing the primary particle diameter of the carbonaceous powder, the pore mode diameter of the microporous layer becomes larger.

[0077] Here, the pore mode diameter of the microporous layer can be obtained by obtaining the pore mode diameter in the range of 0.03 μm or more and less than 1 μm by the same method as the method for measuring the pore mode diameter of the conductive porous substrate.

[0078] In the present invention, the number of pores with a diameter of 150 μm or more on the surface of the microporous layer is preferably in the range of 0.001 to 0.050 per cm 2 If the number of pores is 0.050 per cm 2 or less, in the case of a process of forming a catalyst layer by coating a catalyst coating liquid on the microporous layer, the catalyst coating liquid is not easily infiltrated into the microporous layer and can be uniformly coated. Considering these aspects, the number of pores is more preferably 0.040 per cm 2 or less, and further preferably 0.030 per cm 2 or less. The smaller the number of pores, the more preferable, and it is usually 0.001 per cm 2 or more. The microporous layer with the number of pores of 0.001 to 0.050 per cm 2 can be obtained by the following methods: in the following production method, increasing the density of the conductive porous substrate; increasing the hydrophobicity of the conductive porous substrate to suppress the infiltration of MPL ink in the coating process of the microporous layer; or, reducing the pore mode diameter of the conductive porous substrate; reducing the permeability of the gas diffusion electrode substrate.

[0079] Here, regarding the above-mentioned number of pores, for a region larger than a square with a side length of 1 mm obtained by magnifying the surface of the microporous layer by 100 times or more using an optical microscope, observations are made in 5 or more arbitrarily selected fields of view, and the number of pores with a diameter of 150 μm or more is measured and divided by the measured area. When the shape of the pore is not a perfect circle, the diameter of a perfect circle having the same area as the area of the pore is taken as the diameter of the pore. As the optical microscope, for example, a digital microscope M205C (manufactured by Leica Microsystems Co., Ltd.) can be used.

[0080] In the microporous layer of the present invention, the DBP oil absorption amount of the carbonaceous powder contained is preferably in the range of 156 to 220 mL / 100 g. When the above DBP oil absorption amount is 156 mL / 100 g or more, the viscosity of the MPL coating liquid becomes high, and the infiltration of the MPL ink into the conductive porous substrate is suppressed in the coating process of the microporous layer. As a result, the porosity of the conductive porous substrate becomes high, the gas diffusibility and drainage property become high, and overflow can be further suppressed, and the power generation performance is improved. Considering these aspects, the above DBP oil absorption amount is more preferably 160 mL / 100 g or more, and further preferably 170 mL / 100 g or more. In addition, when the above DBP oil absorption amount is 220 mL / 100 g or less, the dispersibility of the carbonaceous powder is improved, and an MPL ink with high storage stability is obtained. In addition, when the above DBP oil absorption amount is 220 mL / 100 g or less, the secondary particle size of the carbonaceous powder is small, and thus the surface roughness of the microporous layer becomes small. Considering these aspects, the above DBP oil absorption amount is more preferably 210 mL / 100 g or less, and further preferably 200 mL / 100 g or less.

[0081] Here, the above DBP oil absorption amount can be increased by increasing the collision speed of the particles as raw materials during the manufacture of the carbonaceous powder. The DBP oil absorption amount of the carbonaceous powder contained in the MPL coating liquid can be determined in accordance with JIS K6217-4 (2008 revised edition).

[0082] In the present invention, the primary particle size of the carbonaceous powder contained in the microporous layer is preferably in the range of 20 to 39 nm. When the primary particle size is 20 nm or more, the pore mode diameter of the microporous layer becomes larger, the gas diffusivity of the microporous layer becomes higher, and the power generation performance of the gas diffusion electrode substrate is improved. Considering these aspects, the primary particle size is more preferably 23 nm or more, and further preferably 26 nm or more. In addition, when the primary particle size is 39 nm or less, the pore mode diameter of the microporous layer becomes smaller, the microporous layer is not easily crushed, and the short-circuit resistance is improved. In addition, by reducing the pore mode diameter of the microporous layer, it is not easy to become a condensation point of water vapor, and thus overflow is not likely to occur. In addition, in the case of a process of forming a catalyst layer by coating a catalyst coating liquid on the microporous layer, the catalyst coating liquid is not easily infiltrated into the microporous layer and can be uniformly coated. Considering these aspects, the primary particle size is more preferably 37 nm or less, and further preferably 35 nm or less.

[0083] Here, the above-mentioned primary particle size can be obtained by the following method: For a cross-section observation sample prepared using an ion milling device, a photograph is taken using a microscope such as a scanning electron microscope at a magnification of 200,000 times or more, and the diameters of 100 randomly selected primary particles are measured and averaged. As the ion milling device, for example, IM4000 (manufactured by Hitachi High-Technologies Corporation) can be used.

[0084] The microporous layer in the present invention preferably contains fibrous carbides having a fiber diameter of 5 nm or more and 10 μm or less and an aspect ratio of 10 or more. The oxygen / carbon element ratio of the fibrous carbide is preferably 0.020 or more. When the oxygen / carbon element ratio of the fibrous carbide is 0.020 or more, the crystallinity of the fibrous carbide is sometimes low and it becomes soft. Therefore, there is a case where even if the aspect ratio is 10 or more, it is not easily pierced into the electrolyte membrane when used in a polymer electrolyte fuel cell. By making the aspect ratio of the fibrous carbide large, an improvement in the enhancement effect can be expected. Therefore, it is preferably 10 or more, and more preferably 100 or more. Therefore, the shape of the fibrous carbide is preferably fibrous, preferably has a small fiber diameter, preferably 1 μm or less, and more preferably 0.1 μm or less. When the fiber diameter of the fibrous carbide is 5 nm or more and 100 nm or less, the fibrous carbide is not easily pierced into the electrolyte membrane, which is preferable. In addition, when the fiber diameter of the fibrous carbide is 500 nm or more and 10 μm or less, it is easy to obtain a crack suppression effect, which is preferable. The above fiber diameter can be in the range between any two of the above upper and lower limits. In the cross-section of the microporous layer of the present invention, preferably 1000 / mm 2 or more of the above-mentioned fibrous carbides are contained. By containing 1000 / mm 2The above-mentioned fibrous carbide can easily achieve a crack suppression effect. The microporous layer of the present invention preferably contains carbon black, a fluororesin, and the above-mentioned fibrous carbide. By containing carbon black, a fluororesin, and the above-mentioned fibrous carbide, a hydrophobic structure can be uniformly produced, and power generation performance and durability are improved. As such a fibrous carbide, for example, a fibrous carbide obtained by heat-treating an acrylic resin, a styrene resin, cellulose, starch, a polylactic acid resin, etc. can be used.

[0085] The microporous layer in the present invention preferably has substantially no cracks. In the case of having no cracks, it is not easy to become a condensation base point of water vapor, and thus overflow is not likely to occur. In addition, when the electrolyte membrane swells and shrinks according to the operating conditions, deformation in the plane direction is easily suppressed. Further, in the case of adopting a process of forming a catalyst layer by coating a catalyst coating liquid on the microporous layer, the catalyst coating liquid can be uniformly coated. The "substantially crack-free" microporous layer in the present invention means a microporous layer in which obvious cracks cannot be recognized visually. For example, for a region larger than a square with a side length of 1 mm obtained by magnifying the surface of the microporous layer 100 times or more using an optical microscope, when observing and measuring the number of cracks with a length of 100 μm or more in the fields of view of 5 or more arbitrarily selected parts, the number obtained by conversion per 1 cm 2 is 50 pieces / cm 2 or less. Preferably, it is 15 pieces / cm 2 or less, and more preferably 5 pieces / cm 2 or less. As the optical microscope, for example, a digital microscope M205C (manufactured by Leica Microsystems Co., Ltd.) can be used.

[0086] The thickness of the microporous layer in the present invention is preferably 100 μm or less. When it is greater than 100 μm, the diffusivity (permeability, drainage) of gas and water in the gas diffusion electrode itself may decrease, or the resistance may increase. From the viewpoints of improving permeability, drainage, or reducing resistance, the thickness of the microporous layer is preferably 80 μm or less, more preferably 40 μm or less. Considering the porosity and pore size of a general conductive porous substrate and hydrophobicity, in order to cover the roughness of the conductive porous substrate, it is preferably 15 μm or more

[0087] Here, the thickness of the microporous layer refers to the value calculated by observing the cross-section. For example, it can be obtained by the following method: Use an ion milling device to cut the microporous layer or the gas diffusion electrode substrate laminated with the microporous layer in the thickness direction, observe its cross-section (the cross-section in the thickness direction) with SEM, and calculate based on the observed image. As the ion milling device, for example, IM4000 (manufactured by Hitachi High-Technologies Corporation) etc. can be used.

[0088] <Carbonaceous powder>

[0089] In the present invention, the aspect ratio of the carbonaceous powder constituting the microporous layer is preferably less than 20. When the aspect ratio becomes 20 or more, it is more likely to be hooked with each other compared to the case where the aspect ratio is less than 20, so cracks are less likely to occur during drying and / or sintering. However, not only that, fibrous carbon with an aspect ratio of 20 or more sometimes has the following problems: It is likely to pierce through the electrolyte membrane, and local short circuits may occur. In addition, when using fibrous carbon with an aspect ratio of 20 or more, compared with the case of using particulate carbonaceous powder of the same volume, the pore diameter in the microporous layer tends to become larger. In the case of a process of forming a catalyst layer by coating a catalyst coating liquid on the microporous layer, it may sometimes be impossible to uniformly coat the catalyst coating liquid. Therefore, the aspect ratio is more preferably 15 or less, further preferably 10 or less, and particularly preferably 2 or less. As such carbonaceous powder, conductive materials such as carbon black, carbon nanotubes, carbon nanofibers, short cut fibers of carbon fibers, graphene, and graphite can be selected. However, from the viewpoints of small aspect ratio, price, reliability in terms of health, and stability of product quality, it is preferable to use carbon black. In addition, from the viewpoint that the activity of the catalyst is not easily reduced due to less impurities, it is preferable to use acetylene black. It should be noted that by observing the cross-section with a scanning electron microscope, in any arbitrarily selected field of view larger than a square with a side length of 5 μm, if fibrous carbon with an aspect ratio of 20 or more is not confirmed, it is determined that fibrous carbon with an aspect ratio of 20 or more is not included. In the case where fibrous carbon with an aspect ratio of 20 or more can be confirmed in any one field of view, it is determined that fibrous carbon with an aspect ratio of 20 or more is included.

[0090] Regarding the aspect ratio in the present invention, in the case where the carbonaceous powder is fibrous carbon, it represents the average length / average diameter. The average length is obtained as follows: Using a microscope such as a scanning electron microscope or a transmission electron microscope, photographs are taken at a magnification of 1000 times or more, and 10 different fibrous carbons are randomly selected, and their lengths are measured, and the average value is obtained; the average diameter is obtained as follows: Using a microscope such as a scanning electron microscope or a transmission electron microscope, photographs are taken at a magnification of 10000 times or more, and 10 different fibrous carbons are randomly selected, and the length (width) in the direction orthogonal to the fiber axis in the photograph is measured at a length of 0.5 μm along the fiber axis, and the average value of them is taken as its diameter, and the average value of 10 is obtained. In the case where the carbonaceous powder is a plate-like object, it represents the average particle diameter / average thickness. The average particle diameter is obtained as follows: It is measured using a laser diffraction particle size distribution analyzer, and the 50% cumulative diameter in terms of volume is obtained. The average thickness is obtained as follows: Using a microscope such as a scanning electron microscope or a transmission electron microscope, photographs are taken at a magnification of 10000 times or more, and 10 different objects are randomly selected, and their thicknesses are measured, and the average value is obtained. In the case of carbon black, the thickness represents the minimum circumscribed circle diameter / maximum inscribed circle diameter of the primary particles. The minimum circumscribed circle diameter and the maximum inscribed circle diameter are obtained as follows: Using a microscope such as a scanning electron microscope or a transmission electron microscope, photographs are taken at a magnification of 200,000 times or more, and 100 different carbon blacks are randomly selected, and their sizes are measured, and the average value is obtained. As such a scanning electron microscope, for example, S-5500 (manufactured by Hitachi, Ltd.) can be used. It should be noted that in the present invention, in the case where the aspect ratio is greater than 20, it can be uniformly treated as >20.

[0091] <Hydrophobic substance>

[0092] In addition, in order to achieve the bonding function for bonding the aforementioned carbonaceous powders to each other, the suppression of water vapor condensation, the drainage of water, or the moisture retention or heat conduction, the microporous layer of the present invention preferably contains a hydrophobic substance represented by a fluororesin. As the fluororesin contained in the microporous layer, high molecular substances such as polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), and tetrafluoroethylene / ethylene copolymer (ETFE) can be cited.

[0093] In the present invention, the melt viscosity of the aforementioned hydrophobic substance at 380 °C is preferably 10 9 Pa·s or less, more preferably 10 7 Pa·s or less, and still more preferably 10 5Less than Pa·s. This is because, by making the melt viscosity of the polymer substance small, the speed of wetting and spreading on the surface of the carbon fiber in the sintering process is fast, and excellent hydrophobicity can be obtained. As a result, it is easy to suppress water vapor condensation, and in the case of a process of forming a catalyst layer by coating a catalyst coating liquid on the microporous layer, the catalyst coating liquid can be uniformly coated. As such a hydrophobic substance, it can be controlled according to the molecular weight and / or the type of compound. For example, FEP is a preferred mode.

[0094] <Gas diffusion electrode substrate>

[0095] As the conductive porous substrate of the present invention, for example, porous substrates containing carbon fibers such as carbon fiber fabrics, carbon fiber papers, carbon fiber non-woven fabrics, carbon felts, carbon papers, and carbon cloths, foamed sintered metals, metal meshes, and metal expanded meshes can be preferably exemplified. Among them, considering the excellent corrosion resistance, it is necessary to contain carbon fibers, and porous substrates such as carbon felts, carbon papers, and carbon cloths containing carbon fibers are preferably used. Furthermore, considering the excellent characteristics of absorbing dimensional changes in the thickness direction of the electrolyte membrane, that is, "elasticity", it is necessary to contain resin carbide, and a substrate containing resin carbide obtained by bonding a carbon fiber paper with resin carbide, that is, carbon paper, is preferably used.

[0096] In the present invention, from the viewpoint of improving gas diffusibility, it is preferable to reduce the thickness of the conductive porous substrate such as carbon paper. That is, the thickness of the conductive porous substrate such as carbon paper is preferably 220 μm or less, more preferably 150 μm or less, and particularly preferably 120 μm or less. However, when it is too thin, the mechanical strength becomes weak, so in order to facilitate the operation in the manufacturing process, it is usually preferably 70 μm or more.

[0097] <Fuel cell>

[0098] Regarding the unit cell of a solid polymer fuel cell, typically, it is composed of a polymer electrolyte membrane, catalyst layers formed on both sides of the polymer electrolyte membrane, a gas diffusion electrode substrate formed outside the catalyst layer, and two separators sandwiching them. Regarding the microporous layer of the present invention, usually, it is disposed on the surface in contact with the catalyst layer as a part of the gas diffusion electrode substrate or the gas diffusion electrode substrate itself.

[0099] <Manufacturing method of gas diffusion electrode substrate>

[0100] As a method for manufacturing the gas diffusion electrode substrate of the present invention, the following method can be preferably exemplified: After subjecting a conductive porous substrate such as carbon paper to hydrophobic treatment by simultaneously imparting a fluororesin and a hydrophobic processing additive different from the fluororesin, coating MPL ink, drying it, and then performing heat treatment at a temperature higher than the above drying temperature.

[0101] Regarding the method of hydrophobic treatment of a conductive porous substrate, in addition to the treatment technique of mixing a hydrophobic treatment additive into a dispersion containing a fluororesin and impregnating the conductive porous substrate, a coating technique of coating the conductive porous substrate with a fluororesin and a hydrophobic treatment additive by die coating, spraying, etc. can also be applied. It should be noted that after the hydrophobic treatment, a drying process and a sintering process can be applied as needed. Among them, sometimes the infiltration of the components of the microporous layer is excessively suppressed, so it is preferably sintered after the formation of the microporous layer.

[0102] As a method of forming the microporous layer, a method of coating MPL ink by screen printing, rotary screen printing, jet spraying, gravure printing, gravure printing, die coater printing, rod coating, knife coating, blade coating, etc. is preferred.

[0103] In the present invention, it is preferably different from the above-mentioned carbonaceous powder and contains a crack suppression material (which becomes fibrous carbide after heat treatment) with an aspect ratio of 10 or more.

[0104] Regarding the crack suppression material with an aspect ratio of 10 or more of the present invention, it is decomposed and removed by heat treatment at a temperature higher than the drying temperature described below, functions as a crack suppression material that enters between the carbonaceous powders during drying to exert a crack suppression effect, and is decomposed and removed in the subsequent process, so there are no problems such as piercing the electrolyte membrane, and it does not hinder the hydrophobic function of the hydrophobic substance. Here, the "temperature exceeding the drying temperature" refers to a temperature higher than the highest temperature reached during drying. A condition of being 50°C or more higher than the drying temperature is preferred.

[0105] Regarding the content of the crack suppression material with an aspect ratio of 10 or more in the MPL ink of the present invention, relative to the mass of the carbonaceous powder, it is preferably 50% by mass or less, more preferably 30% by mass or less, and further preferably 15% by mass or less. The reason is that the risk of the amount of the crack suppression material that cannot be completely decomposed and removed during heat treatment piercing the electrolyte membrane is reduced. When the above ratio is 0.5% by mass or more, it is easy to obtain a crack suppression effect, so it is preferably 1% by mass or more, more preferably 3% by mass or more.

[0106] By making the aspect ratio of the crack suppression material of the present invention large, an improvement in the enhancement effect can be expected, so it is preferably 50 or more, more preferably 100 or more. Thus, the shape of the crack suppression material is preferably fibrous, and from the viewpoints of dispersibility and / or uniformity and the surface smoothness after decomposition and removal, it is preferably small in fiber diameter, for example, preferably 1 μm or less, more preferably 0.1 μm or less.

[0107] The MPL ink involved in the present invention may contain dispersion media such as water and organic solvents, and may also contain dispersion aids such as surfactants. From the viewpoint of productivity, the concentration of carbonaceous powder in the MPL ink is preferably 5% by mass or more. As the dispersion medium, water is preferred, and among the dispersion aids, a nonionic surfactant is more preferably used.

[0108] Regarding the crack suppression material of the present invention, it is preferably heat-resistant at 150 °C and decomposed and removed at 420 °C. The reason is that when the dispersion medium is water, the drying temperature of the MPL ink is usually 70 to 150 °C, and the crack suppression material is decomposed and removed at a temperature below 420 °C at which ordinary hydrophobic substances (such as fluororesins) do not deteriorate or are not decomposed and removed. As raw materials for such a crack suppression material, for example, acrylic resins, styrene resins, cellulose, starch, polylactic acid resins, etc. can be used. Regarding the decomposition and removal in the present invention, it is preferably reduced to 50% by weight or less, and more preferably reduced to 30% by weight or less.

[0109] After coating the MPL ink on the conductive porous substrate and drying it, the crack suppression material is decomposed and removed. This step can also be the same as the drying step, that is, the temperature is directly increased from the drying temperature, or it can be carried out by other steps. The decomposition and removal of the crack suppression material is preferably carried out at a temperature at which the hydrophobic substance does not decompose and at a temperature at which the water repellent melts and adheres uniformly, and more preferably at a temperature at which the dispersion aid is decomposed and removed. Therefore, heating in air to 300 to 400 °C is a preferred method, and heating to 360 to 400 °C is a more preferred method.

[0110] <Manufacturing method of fuel cell>

[0111] In the manufacturing method of a fuel cell using the microporous layer of the present invention, there are two preferred methods. The first is a preferred method (referred to as the CCM method in the present invention) capable of smoothly forming a catalyst layer: on a polymer electrolyte membrane, a catalyst layer pre-formed on a thin film is transferred to manufacture a polymer electrolyte membrane with a catalyst layer, and the polymer electrolyte membrane with a catalyst layer is sandwiched by a gas diffusion electrode substrate having a microporous layer formed on one surface to manufacture a fuel cell. The second is a method (referred to as the GDE method in the present invention) with excellent productivity due to saving the transfer process: a catalyst coating liquid is coated on a gas diffusion electrode substrate having a microporous layer formed on one surface to manufacture a gas diffusion electrode substrate with a catalyst layer, and the polymer electrolyte membrane is sandwiched by it to manufacture a fuel cell.

[0112] Examples

[0113] Hereinafter, the present invention will be specifically described by way of examples.

[0114] <Evaluation>

[0115] A. Median pore diameter, cumulative pore volume

[0116] Measurement was carried out using Autopore9520 manufactured by Shimadzu Corporation, and the calculation was performed with the surface tension σ of mercury set at 485 dyn / cm and the contact angle between mercury and the microporous layer set at 130°.

[0117] B. Silicon / carbon element ratio, oxygen / carbon element ratio

[0118] Regarding the silicon / carbon element ratio, for the surface of the conductive porous substrate on the side opposite to the side with the microporous layer of the gas diffusion electrode substrate, scanning electron microscope (SEM)-EDX measurement was carried out under the conditions of an accelerating voltage of 20 kV and a magnification of 2000 times, and the average value obtained from more than 10 measurements was calculated.

[0119] C. Porosity of the microporous layer

[0120] Regarding the porosity of the microporous layer, for the sample for cross-sectional observation fabricated using an ion milling device, photos were taken using S-5500 manufactured by Hitachi, Ltd. at a magnification of 1000 times or more, the area of the void part was measured, and the ratio of the area of the void part to the observed area was calculated.

[0121] D. Surface roughness of the microporous layer

[0122] Using the shape measuring machine VR-3200 manufactured by KEYENCE Corporation, in the state where the microporous layer is facing up, it was fixed to the device without floating or wrinkling, and measurement was carried out in a field of view of 48 mm 2 Measurements were performed at any 10 locations on the surface of the microporous layer, and the average value of the arithmetic mean roughness Ra at these 10 locations was used as the surface roughness of the microporous layer.

[0123] E. Number of pores in the microporous layer

[0124] Regarding the surface of the microporous layer, using a digital microscope M205C (manufactured by Leica Microsystems), observations were made at 5 locations in a field of view of 5 mm square, the number of pores with a diameter of 150 μm or more was measured, and the result was divided by the measurement area to obtain the number of pores in the microporous layer.

[0125] F. Analysis of fibrous carbide

[0126] The oxygen / carbon element ratio of the fibrous carbide is determined as follows. Using a sample for cross-sectional observation in the thickness direction of the gas diffusion electrode substrate fabricated by an ion milling device, scanning electron microscope (SEM)-EDX measurement is performed under the conditions of an acceleration voltage of 10 kV and a magnification of 100,000 times to obtain the oxygen / carbon element ratio on the fibrous carbide.

[0127] As the scanning electron microscope, S-5500 manufactured by Hitachi, Ltd. is used. As the energy dispersive X-ray analyzer, EX-220SE manufactured by Horiba, Ltd. is used. As the ion milling device, IM4000 (manufactured by Hitachi High-Technologies Corporation) is used.

[0128] G. Permeability

[0129] For the surface of the conductive porous substrate on the side opposite to the side with the microporous layer of the gas diffusion electrode substrate, using S-5500 manufactured by Hitachi, Ltd., 10 photos are taken at an observation magnification of 200 times. The portion covered with the carbonaceous powder is cut out from the obtained images and binarized using image processing software. Using each of the obtained binarized images, the ratio (%) of the area of the portion covered with the carbonaceous powder to the photographed area is calculated, and its average value is obtained as the above-mentioned permeability.

[0130] H. In-plane gas diffusivity

[0131] The in-plane gas diffusivity is determined as follows: Nitrogen is allowed to flow at a pressure of 5 kPa through the cross-section (cross-section in the thickness direction) of the gas diffusion electrode substrate, and its flow rate (cc / min) is measured. The measurement area is 8 mm in length and 24 mm in width. As the measurement device, a water vapor gas water vapor permeation and diffusion evaluation device MVDP-200C manufactured by Nishika Industry Co., Ltd. is used.

[0132] I. Power generation performance (GDE method)

[0133] A catalyst solution containing platinum-supported carbon (manufactured by Tanaka Precious Metals Industry Co., Ltd., platinum loading: 50% by mass), purified water, "Nafion" (registered trademark) solution (5.0% by mass of "Nation" (registered trademark) manufactured by Aldrich), and isopropyl alcohol (manufactured by Nacalai Tesque, Inc.) was coated on the microporous layer to obtain a gas diffusion electrode substrate with a catalyst layer. The electrolyte membrane (manufactured by DuPont, "Nation" (registered trademark)) was clamped and hot-pressed using this gas diffusion electrode substrate with a catalyst layer to fabricate a membrane electrode assembly (MEA). The MEA was assembled into a fuel cell unit, the cell temperature was set at 80 °C, the fuel utilization efficiency was set at 70%, the air utilization efficiency was set at 40%, and the hydrogen on the negative electrode side and the air on the positive electrode side were humidified so that the dew point was 70 °C for power generation, and the voltage at a current density of 1.5 A / cm 2 was measured.

[0134] (Example 1)

[0135] Using PTFE and a silicone-based hydrophobic processing additive, with a slot die coater, 10% by mass of PTFE and 6% by mass of the hydrophobic processing additive in terms of solid content were attached to a carbon paper with a substrate thickness of 150 μm and a substrate density of 0.3 g / cm 3 and dried at 120 °C.

[0136] Carbon black (CB) with a primary particle size of 35 μm and a DBP oil absorption of 180 mL / 100 g as a carbonaceous powder, FEP as a fluororesin, a surfactant, and purified water as a dispersion medium were mixed and adjusted to be CB / hydrophobic material / surfactant / purified water = 7 parts by mass / 3 parts by mass / 14 parts by mass / 76 parts by mass to prepare MPL ink.

[0137] Using a slot die coater, the MPL ink was coated on the hydrophobically processed carbon paper, dried at 120 °C, and then heat-treated at 380 °C to obtain a gas diffusion electrode substrate.

[0138] The evaluation results of the obtained gas diffusion electrode substrate are shown in Table 1.

[0139] (Example 2)

[0140] Using PTFE and a silicone-based hydrophobic processing additive, with a slot die coater, 10% by mass of PTFE relative to 100% by mass of the conductive porous substrate and 16% by mass of the hydrophobic processing additive in terms of solid content were attached to the same carbon paper as in Example 1 and dried at 120°C. Using the same MPL ink as in Example 1, it was coated on the obtained carbon paper by the same method as in Example 1 and heat-treated, etc., to obtain a gas diffusion electrode substrate.

[0141] The evaluation results of the obtained gas diffusion electrode substrate are shown in Table 1. The power generation performance is good, but the infiltration of the microporous layer is significantly suppressed, so the adhesion at the interface of the conductive porous substrate is slightly weak.

[0142] (Example 3)

[0143] Using PTFE as a fluororesin and a silicone-based hydrophobic processing additive, with a slot die coater, 10% by mass of PTFE relative to 100% by mass of the conductive porous substrate and 10% by mass of the hydrophobic processing additive in terms of solid content were attached to the same carbon paper as in Example 1 and dried at 120°C. As the MPL ink, a substance obtained by adding 1% by mass of pulp with an aspect ratio of 20 as fibrous carbide to the same MPL ink as in Example 1 was used, coated on the obtained carbon paper by the same method as in Example 1, and heat-treated, etc., to obtain a gas diffusion electrode substrate.

[0144] The evaluation results of the obtained gas diffusion electrode substrate are shown in Table 1.

[0145] (Example 4)

[0146] Using PTFE as a fluororesin and a hydrocarbon-based hydrophobic processing additive, with a slot die coater, 10% by mass of PTFE relative to 100% by mass of the conductive porous substrate and 10% by mass of the hydrophobic processing additive in terms of solid content were attached to the same carbon paper as in Example 1 and dried at 120°C. Using the same MPL ink as in Example 3, it was coated on the obtained carbon paper by the same method as in Example 1 and heat-treated, etc., to obtain a gas diffusion electrode substrate.

[0147] The evaluation results of the obtained gas diffusion electrode substrate are shown in Table 1.

[0148] (Example 5)

[0149] Using PTFE and a silicone-based hydrophobic processing additive, with a slot die coater, 10% by mass of PTFE relative to 100% by mass of the conductive porous substrate and 10% by mass of the hydrophobic processing additive in terms of solid content were attached to a substrate with a thickness of 150 μm and a substrate density of 0.3 g / cm3 The carbon felt was dried at 120°C. Using the same MPL ink as in Example 1, it was coated on the obtained carbon paper by the same method as in Example 1, and heat treatment and the like were carried out to obtain a gas diffusion electrode substrate.

[0150] The evaluation results of the obtained gas diffusion electrode substrates are shown in Table 1.

[0151] (Comparative Example 1)

[0152] The carbon paper (TGP-H-060) manufactured by Toray Industries, Inc. with a substrate thickness of 190 μm and a substrate density of 0.45 g / cm 3 was used as the conductive porous substrate. PTFE was used as the fluororesin. Using a slot die coater, 10% by mass of PTFE and 6% by mass of a silicone-based hydrophobic processing additive in terms of solid content were attached relative to 100% by mass of the conductive porous substrate, and it was dried at 120°C. Using the same MPL ink as in Example 1, it was coated on the obtained carbon paper by the same method as in Example 1, and heat treatment and the like were carried out to obtain a gas diffusion electrode substrate.

[0153] The evaluation results of the obtained gas diffusion electrode substrates are shown in Table 1. The MPL ink penetrated into the conductive porous substrate, the pore mode diameter of the conductive porous substrate became smaller, the gas diffusivity decreased, and the power generation performance also decreased.

[0154] (Comparative Example 2)

[0155] Except that a carbon paper with a substrate density of 0.24 g / cm 3 was used as the conductive porous substrate, a gas diffusion electrode substrate was obtained in the same manner as in Comparative Example 1.

[0156] The evaluation results of the obtained gas diffusion electrode substrates are shown in Table 1. Compared with Comparative Example 1, the MPL ink also easily penetrated into the low-density substrate, the pore mode diameter of the conductive porous substrate became smaller, the gas diffusivity decreased, and the power generation performance also decreased. In addition, roughness was generated on the MPL surface. Since the number of pores on the surface of the microporous layer increased, the catalyst coating liquid could not be uniformly coated.

[0157] (Comparative Example 3)

[0158] PTFE was used as the fluororesin. Using a slot die coater, 10% by mass of PTFE and 6% by mass of a silicone-based hydrophobic processing additive in terms of solid content were attached to a carbon paper with a substrate thickness of 150 μm and a substrate density of 0.3 g / cm 3 and dried at 120°C.

[0159] Before coating the MPL ink, the conductive porous substrate was heat-treated at 380 °C. Using the same MPL ink as in Example 1, it was coated on the obtained carbon paper by the same method as in Example 1 and then heat-treated, etc., to obtain a gas diffusion electrode substrate.

[0160] The evaluation results of the obtained gas diffusion electrode substrate are shown in Table 1. Since heat treatment was performed at a high temperature before forming the microporous layer, the manufacturing cost became high and the productivity decreased. In addition, due to the heat treatment before MPL coating, the infiltration of the microporous layer was significantly suppressed excessively, and the adhesion at the interface of the conductive porous substrate was significantly reduced.

[0161] (Comparative Example 4)

[0162] As the conductive porous substrate, carbon paper was obtained by the same method as in Comparative Example 3. Then, as the carbon powder, carbon black (CB) with a primary particle size of 45 μm and a DBP oil absorption of 140 mL / 100 g was used. Except for this, MPL ink was prepared with the same formulation as in Example 1 and coated and heat-treated by the same method as in Example 1 to obtain a gas diffusion electrode substrate.

[0163] The evaluation results of the obtained gas diffusion electrode substrate are shown in Table 1. Since there was a lot of infiltration of the MPL ink, the pore mode diameter of the conductive porous substrate decreased and the power generation performance decreased. Since the number of pores on the surface of the microporous layer increased, the catalyst coating liquid could not be uniformly coated.

[0164] (Comparative Example 5)

[0165] As the conductive porous substrate, carbon paper was obtained by the same method as in Comparative Example 3. Then, using a slot die coater, the same MPL ink as in Example 1 was coated twice and heat-treated by the same method as in Example 1 to obtain a gas diffusion electrode substrate.

[0166] The evaluation results of the obtained gas diffusion electrode substrate are shown in Table 1. Since the MPL ink was coated twice, the manufacturing cost became high and the productivity decreased. In addition, there was a lot of infiltration of the MPL ink, the pore mode diameter of the conductive porous substrate decreased, and the power generation performance decreased.

[0167] (Comparative Example 6)

[0168] Using PTFE, with a slot die coater, 10% by mass of PTFE and 6% by mass of an organosilicon-based hydrophobic processing additive in terms of solid content were attached to the same carbon paper as in Example 1 and dried at 120 °C.

[0169] As the carbonaceous powder, vapor-grown carbon fiber (VGCF) with a fiber diameter of 150 nm, an oxygen / carbon element ratio of 0.005, and an aspect ratio > 20 was used. Other than that, the same MPL ink as in Example 1 was prepared, and coating, heat treatment, etc. were carried out using the same method as in Example 1 to obtain a gas diffusion electrode substrate.

[0170] The evaluation results of the obtained gas diffusion electrode substrate are shown in Table 1. Since the pore mode diameter of the microporous layer is large, more infiltration of the catalyst coating liquid occurs, and it is impossible to uniformly coat the catalyst coating liquid. In addition, since the infiltration of the microporous layer is significantly suppressed, the adhesion at the interface of the conductive porous substrate is significantly reduced. In addition, since VGCF was used, the manufacturing cost became high and the productivity decreased.

[0171] [Table 1]

[0172]

Claims

1. A gas diffusion electrode substrate having a microporous layer on one side of a conductive porous substrate, The conductive porous substrate contains carbon fiber, resin carbide, and fluororesin, and has a density in the range of 0.26 to 0.39 g / cm 3 and the median pore diameter is in the range of 30 to 50 μm. wherein the microporous layer is composed of a single layer containing carbonaceous powder and fluororesin, has a surface roughness of 2.0 to 6.0 μm, a porosity of 50 to 95%, and a pore mode diameter of 0.050 to 0.090 μm, wherein the DBP oil absorption of the carbonaceous powder contained in the microporous layer is 156 to 220 mL / 100 g, and the primary particle size is 20 to 39 nm.

2. The gas diffusion electrode substrate according to claim 1, wherein, The silicon / carbon element ratio in the surface of the conductive porous substrate on the side opposite to the surface having the microporous layer is 0.020 or more.

3. The gas diffusion electrode substrate according to claim 1 or 2, wherein The oxygen / carbon element ratio in the surface of the conductive porous substrate on the side opposite to the surface having the microporous layer is 0.005 or more.

4. The gas diffusion electrode substrate according to claim 1 or 2, wherein When the pore mode diameter of the conductive porous substrate is 30 to 50 μm, the cumulative pore volume per 1 cm 2 is 1.5 to 4.0 μL / cm 2 .

5. The gas diffusion electrode substrate according to claim 1 or 2, wherein The number of pores with a diameter of 150 μm or more on the surface of the microporous layer is 0.001 to 0.050 pores / cm 2 .

6. The gas diffusion electrode substrate according to claim 1 or 2, wherein, The permeability of the carbonaceous powder in the surface of the conductive porous substrate on the side opposite to the surface having the microporous layer of the gas diffusion electrode substrate is less than 10%.

7. The gas diffusion electrode substrate according to claim 1 or 2, having an in-plane gas diffusivity of 40 to 80 cc / min.

8. The gas diffusion electrode substrate according to claim 1 or 2, wherein, The microporous layer further contains fibrous carbide having a fiber diameter of 5 nm or more and 10 μm or less and an aspect ratio of 10 or more.

9. The gas diffusion electrode substrate according to claim 8, wherein, The oxygen / carbon element ratio of the fibrous carbide is 0.020 or more.

10. The method for manufacturing the gas diffusion electrode substrate according to any one of claims 1 to 9, wherein, After simultaneously imparting a fluororesin and a hydrophobic processing additive different from the fluororesin to the conductive porous substrate, an MPL ink is coated. The MPL ink is obtained by dispersing carbonaceous powder, fluororesin particles, and a surfactant in water.

11. The manufacturing method of the gas diffusion electrode substrate according to claim 10, wherein, A hydrophobic processing additive having a mass retention rate of 50% or less when heat-treated at a temperature of 300°C or higher is used.

12. The manufacturing method of the gas diffusion electrode substrate according to claim 10 or 11, wherein, As the hydrophobic processing additive, any one of a silicone-based hydrophobic processing additive, a paraffin-based hydrophobic processing additive, and a hydrocarbon-based hydrophobic processing additive is used. The hydrocarbon-based hydrophobic processing additive is a high molecular compound having a side chain containing a perfluoroalkyl group or a hydrocarbon group in the main chain of an acrylate polymer.

13. A solid polymer fuel cell comprising the following components: A polymer electrolyte membrane; Catalyst layers formed on both sides of the polymer electrolyte membrane; The gas diffusion electrode substrate according to any one of claims 1 to 9 formed outside the catalyst layer; and Two separators sandwiching them.

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