JP2016054066A - Method for producing nonfired gas diffusion layer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of more easily producing a gas diffusion layer.SOLUTION: A method for producing a nonfired gas diffusion layer includes: mixing fluorine-free elastomer resin, a conductive material and an oil-soluble solvent and preparing a liquid mixture; and applying the liquid mixture to a porous substrate, drying the liquid mixture, and forming a porous layer containing the fluorine-free elastomer resin and the conductive material on the porous substrate.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a non-fired gas diffusion layer.

  In recent years, in response to social demands and trends against the background of energy and environmental problems, fuel cells that can operate at room temperature and obtain high output density have attracted attention as power sources for electric vehicles and stationary power sources. A fuel cell is a clean power generation system in which the product of an electrode reaction is water in principle and has almost no adverse effect on the global environment. In particular, a polymer electrolyte fuel cell (PEFC) is expected as a power source for electric vehicles because it operates at a relatively low temperature. The polymer electrolyte fuel cell has a structure in which a plurality of single cells that exhibit a power generation function are stacked. This single cell includes a polymer-electrolyte membrane, a membrane-electrode assembly (MEA) having a pair of catalyst layers and a pair of gas diffusion layers (GDL) that are sequentially formed on both surfaces of the membrane. And MEA which each single cell has is electrically connected with MEA of an adjacent single cell through a separator. Thus, a fuel cell stack is comprised by laminating | stacking a single cell. The fuel cell stack functions as power generation means that can be used for various applications.

  Among the above-mentioned configurations, as the gas diffusion layer, a gas diffusion layer substrate and a microporous layer are known. Here, the microporous layer functions as an intermediate layer for reducing the electrical resistance between the gas diffusion layer and the catalyst layer and improving the gas flow, and is disposed on the catalyst layer side of the gas diffusion layer. The microporous layer is required to be excellent in gas permeability and drainage, together with the gas diffusion layer base material, as in the whole gas diffusion layer.

  In order to satisfy the above requirements, for example, Patent Document 1 discloses the following manufacturing method as a manufacturing method of a gas diffusion layer in which a microporous layer is formed. First, a coating composition in which a powdered conductive material and a water repellent are dispersed in water is applied to a porous substrate and impregnated inside. Thereafter, a coating composition in which a powdered conductive material, a flaky conductive material, and a water repellent are dispersed in water is applied to the gas diffusion layer substrate, and the surface of the porous substrate is microporous. A layer is formed. The gas diffusion layer described in Patent Document 1 can adjust water repellency and drainage according to the blending ratio and size of the flaky conductive material.

JP 2008-59917 A

  However, in the production of the gas diffusion layer described in Patent Document 1, a fluororesin such as PTFE is used as a water repellent (paragraph “0026” in Patent Document 1). For this reason, in order to melt a fluororesin, the baking process at the high temperature normally exceeding 300 degreeC is required (for example, Paragraph "0042" of patent document 1, "0045"). For this reason, when manufacturing a gas diffusion layer, energy cost starts.

  Therefore, the present invention has been made in view of the above circumstances, and an object thereof is to provide a method for manufacturing a gas diffusion layer that can be manufactured at a lower cost.

  Another object of the present invention is to provide a method for producing a gas diffusion layer that can be produced simply (with a small number of steps).

  In order to solve the above-mentioned problems, the present inventors have intensively studied. As a result, it was found that a microporous layer can be formed on a substrate at low cost without the need for a firing step by applying a mixed liquid containing a non-fluorinated elastomer resin and a conductive material to the porous substrate. The present invention has been completed.

  According to the present invention, a porous layer can be formed on a porous substrate by applying and drying a liquid mixture containing a non-fluorine-based elastomer resin and a conductive material on the porous substrate. Do not need. For this reason, a gas diffusion layer can be manufactured cheaply.

It is a schematic sectional drawing which shows the basic composition of the polymer electrolyte fuel cell which concerns on one Embodiment of this invention. It is an expanded section schematic diagram showing one embodiment of a gas diffusion layer (4a, 4c). 3A is a cross-sectional photograph of the gas diffusion layer (1) produced in Example 1, and FIG. 3B is a surface photograph of the gas diffusion layer (1) produced in Example 1. FIG. FIG. 4 is a surface photograph of the gas diffusion layer (2) produced in Example 2. It is a figure which shows the gas-diffusion ability of the gas diffusion layer produced in Examples 1, 2 and Comparative Example 1. It is a figure which shows the electrical resistance of the gas diffusion layer produced in Example 1, 2 and the comparative example 1. FIG.

The method for producing the non-fired gas diffusion layer of the present invention includes the following steps:
(1) A non-fluorinated elastomer resin, a conductive material and a solvent are mixed to prepare a mixed solution (step (1)); and (2) the mixed solution is applied to a porous substrate and then dried. And forming a porous layer containing the non-fluorinated elastomer resin and a conductive material on the porous substrate (step (2)).
Have that. According to the method of the present invention, the gas diffusion layer can be easily produced at a low cost and / or with a small number of steps without requiring a firing step. In addition, the gas diffusion layer produced by the method of the present invention is used as a member of a fuel cell, and is preferably disposed between the catalyst layer and the separator and has high gas permeability and / or drainage. In the present specification, “non-firing” means that a firing step (high-temperature firing step) is not performed during production. Here, the “high temperature firing step” or “baking step” means a heat treatment step at 250 ° C. or higher.

  In the present specification, the non-fired gas diffusion layer is also simply referred to as “the gas diffusion layer of the present invention”. In the present specification, the “non-fluorinated elastomer resin” is also simply referred to as “elastomer resin”. The “porous layer” according to the present invention is also referred to as “gas diffusion porous layer”, “microporous layer”, “microporous layer”, “microporous layer”, or “MPL layer”. The “porous substrate” according to the present invention is also referred to as “gas diffusion substrate” or “gas diffusion layer substrate”.

  As in Patent Document 1, after coating and impregnating a porous substrate with a coating composition containing a powdered conductive material and a water repellent, the coating composition containing the powdered conductive material, the flaky conductive material and the water repellent A method is known in which a product is further applied to form a microporous layer on the surface of a porous substrate. However, the above method requires the coating process to be carried out in two stages, has a large number of processes, and is not desirable from the viewpoint of mass production. In addition, a fluororesin such as PTFE used as a water repellent is expensive and has been a factor in increasing the cost of the fuel cell. In addition, a coating composition containing a fluororesin must be baked at a high temperature after application (see, for example, paragraphs “0042” and “0045” of Patent Document 1). For this reason, the above method has a problem in mass production from the viewpoint of time and energy cost. Further, there is a demerit in that it is necessary to use a substrate (for example, a polyimide film) that can withstand the firing temperature.

  Therefore, the present inventors diligently studied a method that can produce a gas diffusion layer without using a baking step in a system that does not use a fluororesin such as PTFE. As a result, when a mixture of non-fluorinated elastomer resin and conductive material is applied to a porous substrate and dried to form a porous layer on the porous substrate, the porous layer is subjected to a high-temperature baking step. It has been found that the film can be formed on a porous substrate without using it. Since the firing step is unnecessary, it is possible to suppress / prevent the oxidation of the porous base material (carbon paper or the like) due to the firing step and increase the electrical resistance, and it is also possible to suppress / prevent deterioration of the porous base material. For this reason, the gas diffusion layer produced by the method of the present invention can exhibit and maintain high conductivity (excellent in durability). In addition, according to the method of the present invention, a baking step is not required, and a mixed liquid of a non-fluorinated elastomer resin and a conductive substance is directly applied to a porous substrate and dried to form a porous layer. Therefore, it is not necessary to use a heat-resistant base material that can withstand high-temperature firing. For this reason, the cost at the time of producing a microporous layer can be reduced, and also the energy cost at the time of production can be reduced, which is suitable for mass production.

  Further, when a fluororesin is used as a water repellent as in Patent Document 1, it is necessary to use a surfactant for the purpose of dispersing the fluororesin. When the surfactant is water-soluble, the surfactant in the gas diffusion layer is eluted into the catalyst layer by water generated on the cathode side of the polymer electrolyte fuel cell, causing a decrease in performance. It also causes piping corrosion. Further, when the surfactant is ionic, the polymer electrolyte (ionomer) ions contained in the catalyst layer of the solid polymer fuel cell are consumed to lower the conductivity. On the other hand, when forming a porous layer using a non-fluorine-based elastomer resin, the non-fluorine-based elastomer resin is porous in the form of a solution without using a dispersant such as a surfactant as described above. It can be applied to a porous substrate. For this reason, the problem by presence of dispersing agents, such as above-mentioned surfactant, hardly arises at all.

  In addition, when the dispersion of PTFE is used to form a microporous layer, it will settle and the concentration will vary, so it must be stirred before use, but it will solidify if stirred strongly, so it will take time. It was necessary to stir gently. For this reason, there was a difficulty in terms of production efficiency. On the other hand, when a porous layer is formed using a non-fluorine-based elastomer resin, the porous layer can be formed on the porous substrate in one application step (gas diffusion layer can be manufactured). Since the number of steps is small, it can be easily produced. For this reason, the method of this invention is very preferable also from the point of mass production.

  Therefore, the gas diffusion layer manufactured by the method of the present invention can be easily manufactured at a low cost and with a small number of steps without going through the firing step.

  In addition to the above, the gas diffusion layer obtained by the method of the present invention is excellent in gas permeability and drainage. The detailed mechanism by which the gas diffusion layer of the present invention has such gas permeability and drainage is unknown, but is presumed as follows. In addition, this invention is not restrained by the following mechanism at all. When a fluororesin such as PTFE is used for the porous layer (microporous layer), the water repellency is high and the water repellency is high. On the other hand, the coating film containing PTFE and the conductive material applied to the porous base material at the time of manufacturing the gas diffusion layer is baked. At this time, a part of the fluororesin is melted to cover the surface of the conductive material and serve as a binder. Function. However, unmelted PTFE that has not been melted in the firing step does not participate in mass transport at all, reduces the amount of carbon per volume, or unmelted PTFE causes clogging of the gas diffusion layer, Reduce gas permeability.

  On the other hand, according to the present invention, the resin solution of the non-fluorinated elastomer resin penetrates into the porous substrate. By penetration of the non-fluorinated elastomer resin solution into the porous substrate, a thin non-fluorinated elastomer resin film is formed on the porous substrate surface and the pore surface. Since the elastomer resin exhibits water repellency, the gas diffusion layer of the present invention exhibits excellent drainage. Further, due to the water repellency of the elastomer resin, the water repellent treatment of the porous substrate is not necessary. Further, a thin resin film is formed on the pore surface of the porous substrate, and there are no resin particles that cause clogging in the pores. For this reason, the porosity of the porous substrate is substantially maintained as it is, and the porous substrate can maintain high gas diffusibility and gas permeability. Furthermore, a non-fluorinated elastomer resin film is formed on the surface of the conductive material by mixing the non-fluorinated elastomer resin with the conductive material in the form of a solution. For this reason, there is little or no non-fluorinated elastomer resin in the porous layer in the form of particles. For this reason, the porous layer according to the present invention can utilize the gaps between the conductive substances to the maximum, and thus exhibits excellent gas diffusibility and gas permeability. Further, due to the rubber elasticity of the non-fluorine-based elastomer resin, nearby conductive substances are slightly attracted within the porous layer, and the electrical resistance can be further reduced. However, even in this case, since the elastomer resin film is thin, no stress is generated to the extent that the whole is greatly contracted. For this reason, the gas diffusion layer of this invention can ensure sufficient electroconductivity. Therefore, the fuel cell using the gas diffusion layer is excellent in power generation performance.

  Therefore, the gas diffusion layer produced by the method of the present invention can exhibit and maintain high gas diffusivity, gas permeability, drainage, and conductivity.

  Hereinafter, embodiments of the method for producing a gas diffusion layer of the present invention will be described in detail. However, the present invention is not limited only to the following embodiments. In this specification, “X to Y” indicating a range means “X or more and Y or less”. Unless otherwise specified, measurement of operation and physical properties is performed under conditions of room temperature (20 to 25 ° C.) / Relative humidity 40 to 50%.

[Step (1)]
In this step, a non-fluorinated elastomer resin, a conductive substance, and an oil-soluble solvent are mixed to prepare a mixed liquid (dispersion liquid, ink composition).

  Here, the non-fluorinated elastomer resin is not particularly limited, but preferably has water repellency and / or oil solubility, and preferably has both water repellency and oil solubility. When the elastomer resin has water repellency, the porous layer can exhibit further excellent drainage. Further, since the elastomer resin has oil solubility, the elastomer resin film can be more easily formed on the surface of the conductive material using the elastomer resin solution. For this reason, since the presence of the elastomer resin particles in the porous layer can be significantly reduced, the porous layer can exhibit further excellent gas permeability.

  Here, in this specification, “water repellency” means a surface contact angle formed when a water droplet is dropped on a resin formed as a smooth film (in this specification, simply “surface contact angle”). Also referred to as 90 ° or more. Preferably, the surface contact angle of the elastomer resin is preferably 95 ° or more, more preferably 100 ° or more. The upper limit of the surface contact angle of the elastomer resin is not particularly limited, but is preferably 150 ° or less, and more preferably 140 ° or less. In the present specification, the “surface contact angle” or “surface contact angle with respect to water” is a surface contact angle formed when a water droplet is dropped with respect to an elastomer resin formed as a smooth film. The value measured by the method.

(Measurement method of water surface contact angle (surface contact angle))
A porous layer is fixed to a glass plate with a double-sided tape (sample). 3 μl of pure water was dropped onto this sample, and the contact angle 20 seconds after the addition of pure water using an ellipse fitting method was measured using a contact angle measuring device (Auto Dispenser AD-31, DropMaster700, manufactured by Kyowa Interface Chemical Co., Ltd.). taking measurement.

  In the specification, “the elastomer resin has oil solubility” means that the elastomer resin has a solubility of 5% by weight or more with respect to the organic solvent. Here, the organic solvent includes petroleum solvents such as hexane, heptane, toluene, xylene and petroleum benzine, ketone solvents such as acetone, methyl ethyl ketone and cyclohexanone, and ether solvents such as methyl cellosolve, dimethyl cellosolve, tetrahydrofuran and dioxane. Can be mentioned. In the present invention, the elastomer resin is 5 wt.% At 25 ° C. or 30 ° C. with respect to at least one of the above organic solvents, particularly toluene, THF and hexane (preferably two solvents, more preferably all three solvents). % Or more is preferable, and it is more preferable that the solubility is 10% by weight or more. The upper limit of the solubility of the elastomer resin in the organic solvent is not particularly limited as long as the ink composition containing the elastomer resin can be produced, and can be appropriately selected.

  That is, the elastomer resin preferably has a surface contact angle with water of 100 ° or more and / or a solubility with respect to an organic solvent of 5% by weight or more, a surface contact angle with water of 100 ° or more, and an organic solvent. More preferably, the solubility in is 5% by weight or more.

  The elastomer resin used in the present invention is not particularly limited as long as it has rubber elasticity, but preferably exhibits the above water repellency and / or oil solubility. Examples of such elastomer resins include hydrogenated petroleum resins, block copolymers of polystyrene and polyolefin, styrene-butadiene copolymers (SBR resins), acrylonitrile-butadiene copolymers (NBR resins), and acrylonitrile-butadiene-styrenes. A copolymer (ABS resin) etc. are mentioned. The elastomer resin may be used alone or in the form of a mixture of two or more.

  Here, the hydrogenated petroleum resin is not particularly limited, but may have a styrenic structural unit (for example, styrene or methylstyrene) from the viewpoints of suppression / prevention of chemical deterioration, weather resistance, steam resistance, and the like. preferable. Moreover, the hydrogenated petroleum resin which has a styrene-type structural unit is preferable also from the point which has organic-solvent solubility (oil solubility) and moderate elastic modulus (rubber elasticity). In particular, high water repellency and rubber elasticity can be imparted by subjecting a part of the styrene-based structural unit to reduction treatment (hydrogenation) to obtain a polyolefin. As such a hydrogenated petroleum resin, known resins such as JP-A-6-322020 and JP-A-2004-189964 can be used. A commercially available product may be used as the hydrogenated petroleum resin. Specifically, I'mabe (registered trademark) S grade (S-100, S-110) (partially hydrogenated type), Imabe (registered trademark) P grade (P-100, P-125, P-140) (completely) Hydrogenated type) (DCPD (dicyclopentadiene) / aromatic copolymer-based hydrogenated petroleum resin made mainly from C5 fraction) (all manufactured by Idemitsu Kosan Co., Ltd.); Liquid rubber Claprene (registered trademark) LIR (hydrogenation type) (200 (hydrogenation rate = about 100%), 230 (hydrogenation rate = about 100%), 290 (hydrogenation rate = about 90%) (all manufactured by Kuraray Co., Ltd.) Can be mentioned.

The block copolymer of polystyrene and polyolefin can give moderate rubber elasticity by having polyolefin. The block copolymer of polystyrene and polyolefin is not particularly limited, and examples thereof include a block copolymer of polystyrene and at least one olefin polymer such as ethylene, propylene, butylene, and methylpentene. The block copolymer of polystyrene and polyolefin has both a styrene structural unit having crystallinity and organic solvent solubility (oil solubility) and an amorphous polyolefin structural unit having non-crystallinity and organic solvent insolubility, and is 100 ° C. The rubber elasticity can be exhibited in the following. A commercial product may be used as the block copolymer of polystyrene and polyolefin. Specifically, the thermoplastic elastomer SEPTON (registered trademark) SEP series (SEP1001, SEP1020) (polystyrene-poly (ethylene / propylene) block: PS (—CH ₂ —CH (CH ₃ ) —CH ₂ —CH) _2- ) _m (PS represents polystyrene, m represents the number of (ethylene / propylene) blocks), Septon (registered trademark) SEPS series (SEPS 2002, SEPS 2004, SEPS 2005, SEPS 2006, SEPS 2007, SEPS 2104, SEPS 2063) ( polystyrene - poly (ethylene / propylene) block - a _{polystyrene: PS (-CH 2 -CH (CH} 3) -CH 2 -CH 2 -) m PS (PS represents polystyrene, m is (ethylene / propylene) Shows the number of locks), Septon (TM) SEBS series (SEBS8004, SEBS8004, SEBS8006, SEBS8007 , SEBS8076, SEBS8104) ( polystyrene - poly (ethylene / butylene) block - a _{polystyrene: PS [(- CH 2 -CH} 2 - CH ₂ —CH ₂ —) _m — (CH ₂ —CH (CH ₂ CH ₃ ) —) _n ] PS (PS represents polystyrene, m represents the number of (ethylene) blocks, and n represents (butylene) ) Indicates the number of blocks), Septon® SEEPS series (SEEPS 4033, SEEPS 4044, SEEPS 4055, SEEPS 4077, SEEPS 4099) (polystyrene-poly (ethylene-ethylene / propylene) block-polystyrene: PS _{-CH 2 -CH (CH 3) -CH} 2 -CH 2 -) m - (CH 2 -CH 2 -) n PS (PS represents polystyrene, m is (ethylene / propylene) indicates the number of blocks , N represents the number of (ethylene) blocks) (all manufactured by Kuraray Co., Ltd.).

  Similarly, commercially available styrene-butadiene copolymers, acrylonitrile-butadiene copolymers and acrylonitrile-butadiene-styrene copolymers may also be used. Commercially available styrene-butadiene copolymer is not limited to the following, but styrene-butadiene rubber (SBR resin) (Performix, Plastici Dip: components are petroleum naphtha 35% by weight, hexane 18% by weight, toluene 15 Wt%, MEK 5 wt%, SBR (resin) 26 wt%), Toughden (registered trademark) series (manufactured by Asahi Kasei Corporation), Asaprene (registered trademark) series (for example, Asaprene (registered trademark) 610A, 625A, 670A) ) (Manufactured by Asahi Kasei Co., Ltd.). Commercially available products of acrylonitrile-butadiene copolymer include, but are not limited to, acrylonitrile-butadiene rubber (NBR resin) (manufactured by Konishi, Bond G103), cemedine 521 (nitrile rubber, manufactured by Cemedine Co., Ltd.), and the like. Can be mentioned. Examples of the acrylonitrile-butadiene-styrene copolymer include ABS manufactured by Sampleratech and Denka ABS manufactured by Denki Kagaku Kogyo Co., Ltd.

  Among these elastomer resins, in consideration of water repellency, oil solubility, conductive material coverage, etc., the elastomer resin is a hydrogenated petroleum resin, a block copolymer of polystyrene and polyolefin, a styrene-butadiene copolymer, and It is preferably at least one selected from the group consisting of acrylonitrile-butadiene copolymers, and more preferably a hydrogenated petroleum resin, a block copolymer of polystyrene and polyolefin.

  The conductive substance is not particularly limited, but carbon is preferable from the viewpoint of high conductivity. The carbon is not particularly limited, and is conventionally known, such as carbon black, fibrous graphite, rod-like graphite, acicular graphite, plate-like graphite, columnar graphite, flake graphite, spindle-like graphite, spherical graphite, and expanded graphite. These materials can be appropriately employed.

  Among these, the conductive material preferably contains graphite having an aspect ratio, and is at least one selected from the group consisting of rod-like graphite, needle-like graphite, plate-like graphite, columnar graphite, scale-like graphite, and spindle-like graphite. It is more preferable to contain. In the following, the above graphite is also collectively referred to as “specific shape graphite”. As shown in FIG. 2, the specific shape graphite 31 covers (closes) the pores 32 on the surface of the porous substrate 20 along the long side. For this reason, the presence of the specific shape 31 allows the conductive material 33 to pass through the holes 32 and to form holes (not shown) inside the porous substrate 20 even if other small conductive substances 33 are present. Can prevent clogging. Therefore, since the gas diffusion layer of the present invention can secure sufficient pores, the gas permeability and gas diffusibility can be further improved. On the other hand, the length of the short side of the specific shape graphite 32 is short. For this reason, even if such specific shape graphite 32 is applied on the porous substrate, the surface of the porous layer is sufficiently smooth. For this reason, even if it is a case where a porous layer and a catalyst layer are laminated | stacked, both can be laminated | stacked closely. In addition, since the elastomer resin is in the form of a solution, the resin solution (and hence the resin) easily penetrates into the porous substrate surface and the internal pores through the voids between the specific shape graphite. For this reason, even if the porous substrate itself does not have water repellency, a thin non-fluorinated elastomer resin film is formed on the porous substrate surface and the pore surface, and the porous substrate is an elastomer resin. The water repellent treatment. In addition, since graphite has some water repellency, the water repellency of the gas diffusion layer can be further improved. Therefore, the gas diffusion layer of the present invention can exhibit high water repellency and drainage without the water repellent treatment of the porous substrate in advance.

  When specific shape graphite is used as the conductive material, the size of the specific shape graphite is not particularly limited, but the length of the long side is 0.05 to 5 times the pore diameter of the porous substrate. preferable. That is, the conductive material preferably includes a conductive material having a long side length of 0.05 to 5 times the pore diameter of the porous substrate. More preferably, the length of the long side of the specific shape graphite is 0.1 to 1 times the pore diameter of the porous substrate. If it is such a magnitude | size, it can suppress / prevent more effectively that specific shape graphite is caught in the fiber and bending part which comprise a porous base material, obstruct | occludes a void | hole. In addition, because the specific shape graphite covers (closes) the pores on the surface of the porous substrate more effectively along the long side, even when other conductive materials are used, voids due to other conductive materials are used. Hole clogging can be more effectively suppressed / prevented. Therefore, the gas diffusion layer using the specific shape graphite of the above size can improve the gas permeability and gas diffusibility more effectively. Moreover, even if it is such a magnitude | size, the resin solution (hence resin) can penetrate | invade in the porous base material surface and an internal void | hole through the space | gap between specific-shaped graphite. Therefore, the gas diffusion layer can exhibit sufficient water repellency and drainage regardless of the presence or absence of the water repellent treatment of the porous substrate.

  Or although the length of the long side of specific shape graphite is not restrict | limited in particular, Preferably it is 1-50 micrometers, More preferably, it is 10-25 micrometers. Moreover, the length of the short side of the specific shape graphite is not particularly limited, but is preferably 0.01 to 5 μm, more preferably 0.1 to 1 μm. Furthermore, the aspect ratio (= long side length / short side length) of the specific shape graphite is not particularly limited, but is preferably 10 to 1000, and more preferably 20 to 100. If it is such a magnitude | size, it can suppress / prevent more effectively that specific shape graphite is caught in the fiber and bending part which comprise a porous base material, obstruct | occludes a void | hole. In addition, because the specific shape graphite covers (closes) the pores on the surface of the porous substrate more effectively along the long side, even when other conductive materials are used, voids due to other conductive materials are used. Hole clogging can be more effectively suppressed / prevented. Therefore, the gas diffusion layer using the specific shape graphite of the above size can improve the gas permeability and gas diffusibility more effectively. Moreover, even if it is such a magnitude | size, the resin solution (hence resin) can penetrate | invade in the porous base material surface and an internal void | hole through the space | gap between specific-shaped graphite. Therefore, the gas diffusion layer can exhibit sufficient water repellency and drainage regardless of the presence or absence of the water repellent treatment of the porous substrate.

  Here, the size of the specific shape graphite can be measured by a known method. For example, using means such as a scanning electron microscope (SEM), a transmission electron microscope (TEM), or a laser scattering particle size distribution analyzer, a statistically significant number of fields (for example, several to several tens of fields) It can be calculated as an average value of the particle diameter (diameter) of the observed particles. The “particle diameter” means the maximum distance among the distances between any two points on the particle outline. In the present specification, the size of the conductive material (including both specific-shaped graphite and other conductive materials) is measured by the following laser scattering particle size distribution meter unless otherwise specified.

(Method for measuring the size of specific shape graphite)
0.2 g of specific shape graphite is added to 30 ml of a pure aqueous solution containing a dispersion aid (Emulgen 709, manufactured by Kao Co., Ltd.) at a concentration of 0.3% by weight, and stirred at a speed of 450 rpm for 1 minute at room temperature (25 ° C.) A specific shape graphite solution was obtained. About this specific shape graphite solution, the particle diameter of specific shape graphite is measured using the laser diffraction and scattering type particle diameter measuring apparatus (the Nikkiso Co., Ltd. make, Microtrac MT3000). In the obtained particle size distribution, the value indicating the peak is defined as the length (μm) of the long side of the specific shape graphite. Moreover, the short side of specific shape graphite is measured with the following image imaging methods. That is, the specific shape graphite solution is applied to an aluminum plate and dried to form a film. This film is observed with a scanning electron microscope (SEM), and an SEM photograph is taken. Here, a statistically significant number (at least 200, preferably at least 300) of the specific shape graphite photographed standing vertically is selected, and the distance from the end to the end is measured. The average value of the measured values is defined as the short side length (μm) of the specific shape graphite.

  The specific shape graphite may be used alone or in the form of a mixture of two or more.

  As described above, the conductive material preferably includes specific shape graphite, but preferably includes other conductive material in addition to the specific shape graphite. The conductive material in such a case is not particularly limited, but carbon black such as oil furnace black, channel black, lamp black, thermal black, and acetylene black, and oil furnace black are preferably used, and acetylene black and oil furnace are preferable. It is more preferable to use black. Since these other conductive substances act as a conductive additive, the conductivity can be further improved. In addition, these other conductive substances are excellent in electronic conductivity and have few water-soluble and oil-soluble impurities.

  The shape of the other conductive material is not particularly limited, and may have any structure such as a spherical shape, a rod shape, a needle shape, a plate shape, a column shape, an indefinite shape, a flake shape, and a spindle shape. Preferably, the other conductive material is spherical. In addition, the size of the other conductive material is not particularly limited, but considering the effect of improving gas permeability and conductivity, when the other conductive material is spherical, The average particle size (average primary particle size) is preferably 2 to 250 nm, and more preferably 10 to 100 nm. Within such a range, the gas diffusion coefficient is improved, high drainage due to capillary force is obtained, and the contact property with the catalyst layer can be improved.

  Here, the size of the other conductive material can be measured by a known method. For example, using means such as a scanning electron microscope (SEM), a transmission electron microscope (TEM), or a laser scattering particle size distribution analyzer, a statistically significant number of fields (for example, several to several tens of fields) It can be calculated as an average value of the particle diameter (diameter) of the observed particles. The “particle diameter” means the maximum distance among the distances between any two points on the particle outline.

  In addition, other conductive substances may aggregate in the mixed solution to form secondary particles. The average particle size (average secondary particle size) of the secondary particles in such a case is not particularly limited, but is preferably about 0.5 to 25 μm. As a result, the gas diffusion coefficient is improved, high drainage due to capillary force is obtained, and the contact property with the catalyst layer can be improved. In addition, the specific shape graphite hardly or not aggregates in the mixed solution, and is substantially present alone. In this specification, the average secondary particle size of other conductive materials can be measured by a known method, but in this specification, unless otherwise specified, it is measured by the following method.

(Measurement method of average secondary particle size)
Into 30 ml of a pure aqueous solution containing 0.2 g of a conductive substance and a dispersion aid (Emulgen 709, manufactured by Kao) at a concentration of 0.3% by weight, stirring is performed at room temperature (25 ° C.) for 1 minute at a speed of 450 rpm, A conductive substance solution was obtained. About this electroconductive substance solution, the particle diameter (diameter) of an electroconductive substance is measured using the laser diffraction and scattering type particle diameter measuring apparatus (The Nikkiso Co., Ltd. make, Microtrac MT3000). In the obtained particle size distribution, a value indicating a peak is defined as an average secondary particle size (μm) of the conductive material. Note that the conductive material is roughly estimated to be equivalent to a “perfect circle”.

  Commercially available materials can be used as the conductive material, such as Vulcan XC-72, Vulcan P, Black Pearls 880, Black Pearls 1100, Black Pearls 1300, Black Pearls 2000, Legal 400, Ketjen Black manufactured by Lion. EC, oil furnace black such as # 3150 and # 3250 manufactured by Mitsubishi Chemical Corporation; acetylene black such as Denka Black HS100 and AB6 manufactured by Denki Kagaku Kogyo Co., Ltd. and the like. In addition to carbon black, artificial graphite or carbon obtained from organic compounds such as natural graphite, pitch, coke, polyacrylonitrile, phenol resin, furan resin may be used. Further, graphite powder such as graphite graphite ACP series, ACB series, SP series, HOP series; exfoliated graphite powder, spheroidized graphite powder, etc. may be used. In order to improve the corrosion resistance and the like, the other conductive material may be subjected to processing such as graphitization. Other conductive materials may be used alone or in the form of a mixture of two or more.

In addition, the BET specific surface area of the conductive material (including both the specific shape graphite and other conductive materials) is preferably 1 to 300 m ² / g in view of high dispersibility in the mixed solution, More preferably, it is 5-100 m < ² > / g.

  When the conductive material is a mixture of specific shape graphite and other conductive material, the mixing ratio of specific shape graphite and other conductive material is not particularly limited. The mixing ratio of specific shape graphite and other conductive material (specific shape graphite: weight ratio of other conductive material) is preferably 1: 0.5 to 25, and more preferably 1: 2 to 10. With such a mixing ratio, the specific shape graphite can sufficiently improve gas permeability and conductivity while sufficiently closing the pores on the surface of the porous substrate.

  The mixing ratio (weight ratio) of the elastomer resin and the conductive material (including both the specific shape graphite and other conductive materials) is not particularly limited. Considering the gas permeability, drainage, water repellency, mechanical strength, electrical resistance, etc. of the gas diffusion layer, the elastomer resin: conductive material mixing ratio (weight ratio) is preferably 1: 1-10. More preferably, the ratio is more than 1: 1 and 4 or less, and particularly preferably around 1: 2. If it is such a range, an electrical resistance can be reduced and the mechanical strength of a gas diffusion layer (especially porous layer) can fully be ensured. In particular, when the mixing ratio (weight ratio) of elastomer resin: conductive material is about 1: 2, the electrical resistance is 1 / compared to the case where the mixing ratio (weight ratio) of elastomer resin: conductive material is 1: 1. It can be reduced to about 10. In addition, when there is too little mixing amount of an electroconductive substance with respect to elastomer resin, an electrical resistance may increase. On the contrary, if the amount of the conductive material mixed with the elastomer resin is too large, the mechanical strength of the porous layer may be lowered. When the conductive material is a mixture of two or more kinds, the mixing ratio (weight ratio) of elastomer resin: conductive material is the mixing ratio (weight) of the elastomer resin and the total amount of these conductive materials. Ratio).

  The solvent used for preparing the mixed liquid in this step is not particularly limited, but is preferably an oil-soluble solvent (organic solvent). The oil-soluble solvent is not particularly limited as long as it dissolves the elastomer resin, but a solvent having a boiling point of about 40 to 150 ° C. is preferably used. A solvent having a boiling point of 150 ° C. or lower is preferable in terms of cost because a coating film can be formed by drying at a relatively low temperature. Moreover, if it is a solvent whose boiling point is 40 degreeC or more, since evaporation of the solvent at the time of mixing an elastomer resin, an electroconductive substance, and an oil-soluble solvent can be suppressed, the mixture which is easy to apply | coat can be prepared easily. In addition, a well-known technique can be applied to the measurement of the boiling point, and in the case of a simple substance, values described in documents such as a chemical handbook can also be referred to. Examples of such solvents include petroleum solvents such as hexane, heptane, toluene, xylene and petroleum benzine, ketone solvents such as acetone, methyl ethyl ketone and cyclohexanone, and methyl cellosolve, dimethyl cellosolve, tetrahydrofuran (THF) and dioxane. And ether solvents. The amount of the solvent added is not particularly limited, but is preferably such an amount that the concentration of the elastomer resin is 1 to 50% by weight, and more preferably 2.5 to 25% by weight. . If it is such a density | concentration, the mixture which is easy to apply | coat can be prepared easily.

  In this step, the order of addition of the elastomer resin, the conductive material and the oil-soluble solvent is not particularly limited, and all the above components are mixed together; after mixing any of the above components, the remaining components are added. Any of the above components may be mixed sequentially. Preferably, it is preferable to dissolve the elastomer resin in a solvent (preferably an oil-soluble solvent) and then add the conductive substance to the obtained solution. Thereby, the elastomer resin can be easily and uniformly dissolved in the oil-soluble solvent. At this time, it is preferable to stir at a temperature of 250 to 1000 rpm for 5 to 60 minutes while heating a solution obtained by dissolving the elastomer resin in a solvent (preferably an oil-soluble solvent) at 25 to 120 ° C. before adding the conductive substance. Thereby, the elastomer resin can be more uniformly dissolved in the solvent.

  The mixed liquid may further contain additives such as a dispersion aid such as a surfactant, a pore-forming agent, and a viscosity modifier. Or you may add a water-soluble substance to a liquid mixture for the purpose of producing a void | hole in a porous layer.

The water-soluble substance is not particularly limited, but preferably satisfies at least one of the following (a) to (e):
(A) It has sufficient water solubility, specifically, it is water-soluble at room temperature (20 ° C.) and dissolves in 3 ml or more, preferably 5 g or more in 100 ml of water at room temperature (20 ° C.);
(B) Can be pulverized (solid at room temperature and can become a fine powder when pulverized);
(C) Insoluble in oil-soluble solvent that dissolves elastomer resin;
(D) low or no catalyst poisoning ability (does not contain at least one of an amino group, a sulfur atom and a phosphorus atom from the viewpoint of suppression / prevention of catalyst poisoning); and (e) suppression of electrolyte membrane deterioration From the viewpoint of the prevention effect, the content of heavy metal elements, particularly iron and copper, is low or zero.

  From the above viewpoint, sugars such as sucrose and glucose, organic compounds such as citric acid, ascorbic acid and urea; salts of alkali metals and alkaline earth metals such as sodium chloride, sodium carbonate, sodium nitrate and calcium chloride; Examples include inorganic compounds such as acids. Of these, sucrose, glucose, sodium chloride, and sodium carbonate are preferred from the viewpoints of production cost, ease of handling, safety, etc., and sucrose, sodium chloride, and sodium carbonate are more preferred. Here, the shape of the water-soluble substance is not particularly limited, and may take any structure such as a spherical shape (particulate shape), a rod shape, a needle shape, a plate shape, a column shape, an indefinite shape, a flake shape, and a spindle shape. From the viewpoint of, spherical (particulate) is preferable. Moreover, it is preferable that the water-soluble substance is pulverized in advance and classified so as to have a predetermined size before being mixed with the elastomer resin, conductive carbon or solvent. The water-soluble substance can be removed by washing with an aqueous solvent, and a porous layer having a desired pore distribution can be formed. For this reason, by performing the pulverization / classification step, a desired pore distribution (pore diameter, porosity, etc.) can be formed in the obtained porous layer. For this reason, the pulverization / classification conditions for the water-soluble substance are appropriately set in consideration of the desired pore distribution (pore diameter, porosity, etc.) of the porous layer.

  The addition amount of the water-soluble substance is not particularly limited, and is appropriately selected according to a desired pore distribution (particularly porosity). Specifically, the addition amount of the water-soluble substance is preferably 0.01 to 25% by weight, more preferably 0.1 to 5% by weight with respect to the elastomer resin. With such an amount, a desired pore distribution (particularly porosity) can be formed in the porous layer.

  The water-soluble substance can be removed by washing with an aqueous solvent after the following step (2). The aqueous solvent that can be used is not particularly limited as long as it is an aqueous solvent that can wash away water-soluble substances. Specifically, water, lower alcohol solvents such as methanol, ethanol and the like can be used. Of these, water is preferably used from the viewpoint of cost and safety. In addition, the said aqueous solvent may be used independently or may be used with the form of 2 or more types of mixtures. In addition, the condition for washing away the water-soluble substance deposited in the coating film with the aqueous solvent may be any condition as long as the water-soluble substance is sufficiently removed to obtain a desired pore distribution. Specifically, the coating film is washed away with an excessive amount of aqueous solvent (washing); the coating film is immersed in an excessive amount of aqueous solvent, preferably while stirring; the coating film is immersed in an excessive amount of aqueous solvent. For example, ultrasonic treatment can be used. In order to promote elution (removal) of the water-soluble substance, it is preferable to warm the aqueous solvent. The temperature of the aqueous solvent is not particularly limited, but is preferably 25 to 80 ° C, more preferably 30 to 60 ° C. At such a temperature, the water-soluble substance can be easily removed with an aqueous solvent, and the porous layer can be easily peeled (removed) from the substrate.

  After mixing the elastomer resin, conductive material, oil-soluble solvent and water-soluble material if necessary as described above, if necessary, defoaming treatment for the purpose of adjusting to a viscosity suitable for application, You may perform a stirring (stirring) process and a grinding | pulverization process. The defoaming process, the stirring (stirring) process, and the pulverizing process may be performed in any one or in combination of two or more. Among these, the machine used for the stirring (kneading) treatment is not limited to the following, but is a self-revolving stirring defoaming mixer, vacuum stirring defoaming mixer, variable speed stirring defoaming mixer, stirrer (stirrer), ultra A sonic disperser or the like can be used. The stirring (kneading) conditions are not particularly limited as long as the above mixture can be made uniform. The stirring (kneading) speed is preferably 100 to 2000 rpm, more preferably 300 to 1500 rpm. The total stirring (kneading) time is preferably 2 to 15 minutes, more preferably 5 to 30 minutes. Under such conditions, the mixture can be sufficiently homogenized. In addition, the machine used for the pulverization is not limited to the following, but is a milling device that gives impact with a spherical media such as a ball mill or a bead mill, a device that applies a shear stress in a roller gap such as a two-roll or three-roll, a homogenizer A device that rotates stirring blades such as a mixer or a jet mill device that collides the objects to be crushed can be used. What is necessary is just to set grinding | pulverization conditions suitably. For example, the pulverization treatment is preferably performed at 3000 to 30000 rotations / minute for 1 to 30 minutes, more preferably 5000 to 15000 rotations / minute for 1 to 10 minutes. In addition, the said grinding | pulverization process changes with apparatuses to be used, and the said conditions (especially rotation speed) are applicable suitably when using a homogenizer especially. Under such conditions, the water-soluble substance and the conductive substance can be pulverized to a desired size, and the mixture can be sufficiently homogenized.

  Moreover, you may filter for the purpose of removing a coarse particle, after performing the said deaeration process, stirring (stirring) process, or a grinding | pulverization process. The filtration method may be natural filtration performed at normal pressure, suction filtration, pressure filtration, or centrifugal filtration.

[Step (2)]
In this step, the liquid mixture (dispersion liquid, ink composition) prepared in the above step (1) is applied to a porous substrate, and then dried to obtain a porous layer containing the non-fluorinated elastomer resin and a conductive substance. Is formed on the porous substrate.

  After the mixture is applied to the porous substrate, the elastomeric resin is adsorbed to the conductive material by drying, and the oil-soluble solvent in the mixed solution volatilizes (evaporates). It is thought to cover. Moreover, since the resin solution (and hence the resin) penetrates into the surface of the porous substrate and the pores in the application step, the application step can be a water repellent treatment step of the porous substrate. For this reason, the porous substrate does not need to be subjected to water repellent treatment in advance. In addition, when using a water-soluble substance, it is thought that a water-soluble substance precipitates and exists between electroconductive substances in the state of a solid uniformly in a coating film.

  The porous substrate used is not particularly limited, and a porous substrate used as a conventional gas diffusion layer substrate can be used. In a system using conventional PTFE, it is necessary to separately use a base material (for example, a polyimide film) that can withstand high-temperature baking in a subsequent process, which is a cause of high cost. On the other hand, according to the method of the present invention, it is not necessary to use such a base material, and the conventional gas diffusion layer base material can be used as the porous base material, so that the production cost of the gas diffusion layer can be reduced. . In addition, as described above, the conventional gas diffusion layer base material is usually subjected to water repellency treatment. However, in the method of the present invention, the water repellency treatment can be omitted, thereby further reducing the production cost of the gas diffusion layer. it can.

  Examples of the porous substrate include carbon-based fabrics made of carbon fibers such as carbon paper and carbon cloth, sheet-like materials having conductivity and porosity such as paper-like paper bodies, felts, and nonwoven fabrics; , Foam metal, expanded metal, punching metal, etching plate, precision press-worked plate, metal mesh, metal wire sintered body, metal nonwoven fabric and the like.

  The porous substrate has pores. Here, the pore diameter of the porous substrate is not particularly limited, but is preferably 10 to 200 μm, and more preferably 50 to 150 μm. With such a pore diameter, the conductive material does not substantially cause clogging of the pores of the porous substrate. Here, the pore diameter of the porous substrate can be measured by a known method, but in this specification, unless otherwise specified, it is measured by the following method.

(Measurement method of pore diameter of porous substrate)
The pore diameter of the porous substrate is measured according to the following bubble point method (based on JIS K3832-1990). That is, a porous base material is cut into a diameter of 25 mm to prepare a sample. This sample is immersed as a test solution in 10 ml of a surfactant solution (Gullwick solution, 15.9 dyn / cm) at room temperature (25 ° C.) for 30 minutes. Next, the sample impregnated in this manner was set in a palm porometer device (manufactured by PMI), a pore size distribution measurement test was performed, and the pore distribution of the sample was measured. The center value (μm) of the pore size distribution is obtained from the obtained pore distribution, and this value is taken as the pore size of the porous substrate. The composition of the GALWICK solution is propylene, 1,1,2,3,3,3 oxide hexahydrofluoric acid (Porous Materials, Inc.).

  The thickness of the porous base material may be appropriately determined in consideration of the characteristics of the obtained gas diffusion layer, but may be about 30 to 500 μm. If the thickness of the substrate is within such a range, the balance between mechanical strength and diffusibility such as gas and water can be appropriately controlled.

  The porous substrate does not necessarily need to be subjected to water repellent treatment in advance, but may contain a water repellent. The water repellent is not particularly limited, and is a fluorine-based polymer such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer (FEP). Conventionally known water repellents such as molecular materials, polypropylene, and polyethylene may be used. The water repellent treatment method is not particularly limited, and may be performed using a general water repellent treatment method. For example, after immersing the base material used for a gas diffusion layer in the dispersion liquid of a water repellent agent, the method of heat-drying with oven etc. is mentioned. Alternatively, a sheet body in which a porous body of polytetrafluoroethylene (PTFE) is impregnated with carbon particles and sintered may be used. By using the sheet body, the manufacturing process is simplified, and handling and assembly when the members of the fuel cell are stacked are facilitated.

  The porous substrate may have other additives. Examples of the additive include conductive carbon, a dispersant, and a dispersion aid.

  The coating thickness of the mixed solution is not particularly limited. Specifically, it is preferable to control the thickness of the porous layer after drying as follows.

  A method for applying the mixed solution is not particularly limited, and a conventionally known method such as spray coating, spin coating, bar coating, blade coating, or the like can be used.

  After applying the mixed solution, it is preferably dried. The drying conditions may be set as appropriate, but the drying temperature is preferably less than 10 to 150 ° C, and preferably 25 to 40 ° C. The drying time is preferably 2 to 30 minutes. According to the method of the present invention, it is not necessary to perform baking after coating and drying of the base material, which is necessary when a PTFE solution is used. If firing is necessary, it is disadvantageous in terms of energy costs. Therefore, in this invention, a baking process is not included in a process (2). Here, a baking process refers to the process of processing for 15 minutes-3 hours at the temperature of 250 degreeC or more, for example, 250-400 degreeC.

  Here, after drying, a hot press may be performed. Hot pressing is preferable because the carbon particles are easily bonded to each other and the toughness of the porous layer is increased. The conditions for the hot press are not particularly limited, and may be set as appropriate in consideration of the type of coated substrate, the type of polymer material, and the content of conductive carbon. The temperature is preferably from room temperature to the base material deformation temperature, more preferably from 100 to 150 ° C. Moreover, it is preferable that it is 0.2-2 Mpa, and, as for a hot press pressure, it is more preferable that it is 0.5-1 Mpa. The hot press time is preferably 0.2 to 1 minute, and more preferably 0.3 to 0.5 minute.

  The thickness of the porous layer is not particularly limited, and may be appropriately determined in consideration of gas diffusibility and resistance. The thickness (dry film thickness) of the porous layer is preferably 20 to 500 μm, more preferably 50 to 400 μm. If it is in such a range, the balance of mechanical strength, gas permeability, and drainage can be appropriately controlled. In the present specification, “the thickness of the porous layer” means the thickness of a layer containing a non-fluorinated elastomer resin and a conductive substance. For example, as in the following examples, a part of the mixed solution may permeate into the porous substrate during the application in this step, and a porous layer may be formed near the surface of the porous substrate. In such a case, the sum of the thickness of the porous layer portion formed in the vicinity of the surface of the porous substrate and the thickness of the porous layer portion formed on the porous substrate is expressed as “the thickness of the porous layer”. And

  By the above manufacturing method, a porous layer containing an elastomer resin and a conductive substance is formed on the porous substrate, and a gas diffusion layer is obtained. Here, since the elastomer resin exhibits water repellency, it can impart excellent drainage to the porous layer. Moreover, the elastomer resin film can be formed on the surface of the conductive material by mixing the solution of the elastomer resin with the conductive material. In addition, since the elastomer resin is applied to the porous substrate in the form of a solution, the elastomer resin can also penetrate into the porous substrate and form an elastomer resin film on the pore surface of the porous substrate. Since there is little or no elastomer resin in the form of particles, the volume that does not contribute to substance (fuel gas or oxidant gas) diffusion can be reduced. Therefore, excellent gas permeability can be imparted to the gas diffusion layer (porous layer and porous substrate). In addition, in the porous layer, the nearby conductive material is slightly attracted by the rubber elasticity of the elastomer resin, and the electrical resistance can be further reduced. However, even in this case, since the elastomer resin film is thin, no stress is generated to the extent that the whole is greatly contracted. For this reason, high conductivity can be imparted to the porous layer.

  Furthermore, since an elastomer resin is used, high-temperature baking at 250 ° C. or higher is not necessary when forming the porous layer, and there is no need to use a heat-resistant substrate that can withstand high-temperature baking. For this reason, the cost at the time of producing a microporous layer can be reduced, and also the energy cost at the time of production can be reduced. Since the material can be input in one step, there is an advantage that productivity is improved and it is suitable for mass production.

  A gas diffusion layer is obtained through the manufacturing method as described above. The thickness of the obtained gas diffusion layer is preferably 50 to 500 μm, and more preferably 100 to 300 μm.

In the gas diffusion layer thus obtained, the elastomer resin dissolved in the solvent penetrates into the porous base material to form a resin film on the surface or the surface of the pores. For this reason, since the porous substrate ensures sufficient pores, the gas diffusion layer produced by the method of the present invention is excellent in gas diffusibility and gas permeability. Specifically, the gas diffusion layer produced by the method of the present invention preferably has a Gurley air permeability of 0.01 to 200 (cc / cm ² / sec), more preferably 0.1 to 100 (cc / Cm ² / sec). In the present specification, “Gurley air permeability (cc / cm ² / sec)” is a value measured by the method described in the following examples.

Further, the permeation time of the gas diffusion layer produced by the method of the present invention is preferably more than 0 seconds and 5 seconds or less, more preferably 0.1 to 3 seconds, and / or the method of the present invention. The gas permeability of the gas diffusion layer produced by is preferably 1 × 10 ⁻¹³ m ² or more, more preferably 5 × 10 ⁻¹³ to 1 × 10 ⁻¹¹ m ² . In this specification, “permeation time” and “gas permeability” are values measured by the methods described in the following examples.

  Moreover, since the gas diffusion layer obtained in this way contains an elastomer resin having excellent water repellency, it is also excellent in water repellency (drainage). Specifically, the surface contact angle with respect to water of at least one surface of the non-fired gas diffusion layer according to the present invention is preferably 110 ° or more. More preferably, the surface contact angle with respect to water of at least one surface of the non-fired gas diffusion layer according to the present invention is preferably 100 to 160 °, more preferably 110 to 155 °, and particularly preferably 120 to 150 °. It is.

  The gas diffusion layer according to the present invention can be preferably applied to a membrane electrode assembly (MEA) and a fuel cell. Accordingly, the present invention provides a non-fired gas diffusion layer produced by the method of the present invention, a membrane electrode assembly (MEA) having the gas diffusion layer, particularly a fuel cell membrane electrode assembly, and the membrane electrode assembly. Including a fuel cell.

  The gas diffusion layer is used as a member of a fuel cell. Hereinafter, a fuel cell using a gas diffusion layer will be described.

[Fuel cell]
A fuel cell includes a membrane electrode assembly (MEA), a pair of separators including an anode side separator having a fuel gas flow path through which fuel gas flows and a cathode side separator having an oxidant gas flow path through which oxidant gas flows. Have.

  FIG. 1 is a schematic diagram showing a basic configuration of a polymer electrolyte fuel cell (PEFC) 1 according to an embodiment of the present invention. The PEFC 1 first includes a solid polymer electrolyte membrane 2 and a pair of catalyst layers (an anode catalyst layer 3a and a cathode catalyst layer 3c) that sandwich the membrane. The laminate of the solid polymer electrolyte membrane 2 and the catalyst layers (3a, 3c) is further sandwiched between a pair of gas diffusion layers (GDL) (anode gas diffusion layer 4a and cathode gas diffusion layer 4c). Thus, the polymer electrolyte membrane 2, the pair of catalyst layers (3a, 3c), and the pair of gas diffusion layers (4a, 4c) constitute a membrane electrode assembly (MEA) 10 in a stacked state. Here, the anode gas diffusion layer 4a and the cathode gas diffusion layer 4c have a porous layer on the catalyst layer (3a, 3c) side.

  In PEFC1, the MEA 10 is further sandwiched between a pair of separators (anode separator 5a and cathode separator 5c). In FIG. 1, the separators (5 a, 5 c) are illustrated so as to be positioned at both ends of the illustrated MEA 10. However, in a fuel cell stack in which a plurality of MEAs are stacked, the separator is generally used as a separator for an adjacent PEFC (not shown). In other words, in the fuel cell stack, the MEAs are sequentially stacked via the separator to form a stack. In an actual fuel cell stack, gas seal portions (gaskets) are disposed between the separators (5a, 5c) and the solid polymer electrolyte membrane 2 or between the PEFC 1 and another adjacent PEFC. However, these descriptions are omitted in FIG.

  The separators (5a, 5c) are obtained, for example, by forming a concavo-convex shape as shown in FIG. 1 by subjecting a thin plate having a thickness of 0.5 mm or less to a press treatment. The convex part seen from the MEA side of the separator (5a, 5c) is in contact with the MEA 10. Thereby, the electrical connection with MEA10 is ensured. Further, a recess (space between the separator and the MEA generated due to the concavo-convex shape of the separator) viewed from the MEA side of the separator (5a, 5c) is a gas for circulating gas during operation of the PEFC 1 Functions as a flow path. Specifically, fuel gas (for example, hydrogen) is circulated through the anode gas channel 6a of the anode separator 5a, and oxidant gas (for example, air) is circulated through the cathode gas channel 6c of the cathode separator 5c. Let

  On the other hand, the recess viewed from the side opposite to the MEA side of the separator (5a, 5c) serves as a refrigerant flow path 7 for circulating a refrigerant (for example, water) for cooling the PEFC during operation of the PEFC 1. . Further, the separator is usually provided with a manifold (not shown). This manifold functions as a connection means for connecting cells when a stack is formed. With such a configuration, the mechanical strength of the fuel cell stack can be ensured.

  In addition, in embodiment shown in FIG. 1, the separator (5a, 5c) is shape | molded by the uneven | corrugated shape. However, the separator is not limited to such a concavo-convex shape, and may be any form such as a flat plate shape and a partially concavo-convex shape as long as the functions of the gas flow path and the refrigerant flow path can be exhibited. Also good.

  In addition, it is preferable that a porous layer is arrange | positioned at least on the catalyst layer (3a, 3c) side.

  Further, the porous layer may be provided in either one of the anode gas diffusion layer and the cathode gas diffusion layer, or may be provided in both of them, but since water is generated on the cathode side, at least on the cathode side. It is preferable to provide a porous layer in both gas diffusion layers.

  The gas diffusion layers (anode gas diffusion layer 4a, cathode gas diffusion layer 4c) are catalyst layers (3a, 3c) of gas (fuel gas or oxidant gas) supplied via the gas flow paths (6a, 6c) of the separator. ) And a function as an electron conduction path.

[Catalyst layer]
The catalyst layers (the anode catalyst layer 3a and the cathode catalyst layer 3c) are layers in which the cell reaction actually proceeds. Specifically, the oxidation reaction of hydrogen proceeds in the anode catalyst layer 3a, and the reduction reaction of oxygen proceeds in the cathode catalyst layer 3c.

  The catalyst layer includes a catalyst component, a conductive catalyst carrier (conductive carrier) that supports the catalyst component, and an electrolyte. Hereinafter, a composite in which a catalyst component is supported on a catalyst carrier is also referred to as an “electrode catalyst”.

  The catalyst component used in the anode catalyst layer is not particularly limited as long as it has a catalytic action in the oxidation reaction of hydrogen, and a known catalyst can be used in the same manner. The catalyst component used in the cathode catalyst layer is not particularly limited as long as it has a catalytic action for the oxygen reduction reaction, and a known catalyst can be used in the same manner. Specifically, it may be selected from metals such as platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, and alloys thereof. .

  Among these, those containing at least platinum are preferably used in order to improve catalyst activity, poisoning resistance to carbon monoxide and the like, heat resistance, and the like. Although the composition of the alloy depends on the type of metal to be alloyed, the content of platinum is preferably 30 to 90 atomic%, and the content of the metal to be alloyed with platinum is preferably 10 to 70 atomic%. In general, an alloy is a generic term for a metal element having one or more metal elements or non-metal elements added and having metallic properties. The alloy structure consists of a eutectic alloy, which is a mixture of the component elements as separate crystals, a component element completely melted into a solid solution, and a component element composed of an intermetallic compound or a compound of a metal and a nonmetal. There is what is formed, and any may be sufficient. At this time, the catalyst component used in the anode catalyst layer and the catalyst component used in the cathode catalyst layer can be appropriately selected from the above. In the present specification, unless otherwise specified, descriptions of the catalyst components for the anode catalyst layer and the cathode catalyst layer have the same definition for both. Therefore, they are collectively referred to as “catalyst components”. However, the catalyst components of the anode catalyst layer and the cathode catalyst layer do not have to be the same, and can be appropriately selected so as to exhibit the desired action as described above.

  The shape and size of the catalyst component are not particularly limited, and the same shape and size as known catalyst components can be adopted. For example, the catalyst component may be granular, scale-like, or layered, but is preferably granular. At this time, the average particle diameter of the catalyst particles is preferably 1 to 30 nm, more preferably 1 to 10 nm, still more preferably 1 to 5 nm, and particularly preferably 2 to 4 nm. When the average particle diameter of the catalyst particles is within such a range, the balance between the catalyst utilization rate related to the effective electrode area where the electrochemical reaction proceeds and the ease of loading can be appropriately controlled. The “average particle diameter of the catalyst particles” in the present invention is the crystallite diameter determined from the half-value width of the diffraction peak of the catalyst component in X-ray diffraction, or the particle diameter of the catalyst component determined by a transmission electron microscope (TEM). It can be measured as an average value of.

  The catalyst component described above is preferably contained in the catalyst layer as an electrode catalyst supported on a conductive carrier.

  The conductive carrier functions as a carrier for supporting the above-described catalyst component and an electron conduction path involved in the transfer of electrons between the catalyst component and another member. Any conductive carrier may be used as long as it has a specific surface area for supporting the catalyst particles in a desired dispersed state and has sufficient electronic conductivity as a current collector. The main component is carbon. Is preferred. Specific examples include conductive materials made of carbon black, activated carbon, coke, natural graphite, artificial graphite and the like. “The main component is carbon” means that the main component contains carbon atoms, and is a concept that includes both carbon atoms and substantially carbon atoms. In some cases, elements other than carbon atoms may be included in order to improve the characteristics of the fuel cell. In addition, being substantially composed of carbon atoms means that mixing of impurities of about 2 to 3% by weight or less is allowed.

The BET specific surface area of the conductive carrier may be a specific surface area sufficient to carry the catalyst component in a highly dispersed state, but is preferably 20 to 1600 m ² / g, more preferably 80 to 1200 m ² / g. Good. When the specific surface area is in the above range, the catalyst component and the polymer electrolyte are sufficiently dispersed in the conductive support to obtain sufficient power generation performance, and the catalyst component and the polymer electrolyte can be used sufficiently effectively.

  In addition, the size of the conductive carrier is not particularly limited, but from the viewpoint of controlling the ease of loading, catalyst utilization, and the thickness of the electrode catalyst layer within an appropriate range, the average particle size is 5 to 200 nm, The thickness is preferably about 10 to 100 nm.

  In the electrode catalyst in which the catalyst component is supported on the conductive support, the supported amount of the catalyst component is preferably 10 to 80% by weight, more preferably 30 to 70% by weight, based on the total amount of the electrode catalyst. . When the supported amount of the catalyst component is within such a range, the balance between the degree of dispersion of the catalyst component on the catalyst support and the catalyst performance can be appropriately controlled. The amount of the catalyst component supported can be examined by inductively coupled plasma emission spectroscopy (ICP).

  The catalyst layer includes an ion conductive polymer electrolyte in addition to the electrode catalyst. The polymer electrolyte is not particularly limited, and conventionally known knowledge can be referred to as appropriate. For example, the ion exchange resin which comprises the following electrolyte layer can be added to a catalyst layer as a polymer electrolyte.

  The polymer electrolyte is not particularly limited, and conventionally known knowledge can be referred to as appropriate. Polymer electrolytes are roughly classified into fluorine-based polymer electrolytes and hydrocarbon-based polymer electrolytes depending on the type of ion exchange resin that is a constituent material. In addition, since the specific description of the fluorine-based polymer electrolyte and the hydrocarbon-based polymer electrolyte is the same as the description of the solid polymer electrolyte membrane below, the description is omitted here. Among these, the polymer electrolyte preferably contains a fluorine atom because it is excellent in heat resistance, chemical stability, and the like. Particularly preferred are fluorine-based electrolytes such as Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.), and the like.

  The content of the polymer electrolysis weight in the catalyst layer is not particularly limited, but the ratio of the polymer electrolysis weight to carbon in the electrode catalyst is preferably 0.3 to 1.2.

  The catalyst component can be supported on the conductive carrier by a known method. For example, known methods such as impregnation method, liquid phase reduction support method, evaporation to dryness method, colloid adsorption method, spray pyrolysis method, reverse micelle (microemulsion method) can be used. Alternatively, a commercially available electrode catalyst may be used.

  The method for forming the catalyst layer is not particularly limited, but preferably a method for forming the catalyst layer by applying a catalyst ink comprising the electrode catalyst, polymer electrolyte and solvent as described above to the surface of the polymer electrolyte membrane. Is mentioned. In this case, the solvent is not particularly limited, and usual solvents used for forming the catalyst layer can be used in the same manner. Specifically, lower alcohols such as water, cyclohexanol, ethanol, 1-propanol and 2-propanol can be used. Further, the amount of the solvent used is not particularly limited, and a known amount can be used. In the catalyst ink, the electrocatalyst is used in any amount as long as it can sufficiently exhibit the desired action, that is, the action of catalyzing the hydrogen oxidation reaction (anode side) and the oxygen reduction reaction (cathode side). May be. It is preferable that the electrode catalyst is present in the catalyst ink in an amount of 5 to 30% by weight, more preferably 9 to 20% by weight.

  The preparation method of the catalyst ink is not particularly limited as long as the electrode catalyst, the electrolyte and the solvent, and if necessary, the water-repellent polymer and / or the thickener are appropriately mixed. For example, a catalyst ink can be prepared by adding an electrolyte to a polar solvent, heating and stirring the mixed solution to dissolve the electrolyte in the polar solvent, and then adding an electrode catalyst thereto. Alternatively, after the electrolyte is once dispersed / suspended in a solvent, the dispersion / suspension may be mixed with an electrode catalyst to prepare a catalyst ink. In addition, a commercially available electrolyte solution (for example, DuPont Nafion solution: Nafion dispersed / suspended at a concentration of 5 wt% in 1-propanol) in which the electrolyte is previously prepared in the above other solvent is used as it is. May be used in the method.

  Each catalyst layer is formed by applying the catalyst ink as described above on the polymer electrolyte membrane or the gas diffusion layer. At this time, the conditions for forming the cathode / anode catalyst layer on the polymer electrolyte membrane are not particularly limited, and can be used in the same manner as known methods or appropriately modified. For example, the catalyst ink is applied onto the polymer electrolyte membrane so that the thickness after drying becomes a desired thickness, and is 25 to 150 ° C., more preferably 60 to 120 ° C. in a vacuum dryer or under reduced pressure. And drying for 5 to 30 minutes, more preferably for 10 to 20 minutes. In addition, in the said process, when the thickness of a catalyst layer is not enough, the said application | coating and drying process is repeated until it becomes desired thickness.

Further, the catalyst content per unit catalyst coating area (mg / cm ² ) is not particularly limited, but in view of sufficient dispersion of the catalyst on the carrier, power generation performance, etc., 0.01 to 1.0 mg / cm ² . However, when the catalyst contains platinum or a platinum-containing alloy, the platinum content per unit catalyst coating area is preferably 0.5 mg / cm ² or less. The use of expensive noble metal catalysts typified by platinum (Pt) and platinum alloys has become a high cost factor for fuel cells. Therefore, it is preferable to reduce the amount of expensive platinum used (platinum content) to the above range and reduce the cost. The lower limit is not particularly limited as long as power generation performance is obtained, and is, for example, 0.01 mg / cm ² or more. In this specification, inductively coupled plasma emission spectroscopy (ICP) is used for measurement (confirmation) of “catalyst (platinum) content per unit catalyst application area (mg / cm ² )”. A person skilled in the art can easily carry out a method of making the desired “catalyst (platinum) content per unit catalyst coating area (mg / cm ² )”, and control the ink composition (catalyst concentration) and coating amount. You can adjust the amount.

  The thickness of the catalyst layer is preferably 0.5 to 30 μm, more preferably 1 to 20 μm, and still more preferably 2 to 15 μm. In addition, the said thickness is applied to both a cathode catalyst layer and an anode catalyst layer. The thickness of the cathode catalyst layer and the anode catalyst layer may be the same or different.

[Solid polymer electrolyte membrane]
The solid polymer electrolyte membrane 2 has a function of selectively allowing protons generated in the anode catalyst layer 3a during operation of the PEFC 1 to permeate the cathode catalyst layer 3c along the film thickness direction. The solid polymer electrolyte membrane 2 also has a function as a partition wall for preventing the fuel gas supplied to the anode side and the oxidant gas supplied to the cathode side from being mixed.

  The solid polymer electrolyte membrane 2 is roughly classified into a fluorine-based polymer electrolyte membrane and a hydrocarbon-based polymer electrolyte membrane depending on the type of ion exchange resin that is a constituent material. Examples of ion exchange resins constituting the fluorine-based polymer electrolyte membrane include Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.), and the like. Perfluorocarbon sulfonic acid polymer, perfluorocarbon phosphonic acid polymer, trifluorostyrene sulfonic acid polymer, ethylene tetrafluoroethylene-g-styrene sulfonic acid polymer, ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride- Examples include perfluorocarbon sulfonic acid polymers. From the viewpoint of improving power generation performance such as heat resistance and chemical stability, these fluorine-based polymer electrolyte membranes are preferably used, and particularly preferably fluorine-based polymer electrolytes composed of perfluorocarbon sulfonic acid polymers. A membrane is used.

  Specific examples of the hydrocarbon electrolyte include sulfonated polyethersulfone (S-PES), sulfonated polyaryletherketone, sulfonated polybenzimidazole alkyl, phosphonated polybenzimidazole alkyl, sulfonated polystyrene, and sulfonated poly. Examples include ether ether ketone (S-PEEK) and sulfonated polyphenylene (S-PPP). These hydrocarbon-based polymer electrolyte membranes have manufacturing advantages such as low cost raw materials, simple manufacturing processes, and high material selectivity.

  In addition, as for the ion exchange resin mentioned above, only 1 type may be used independently and 2 or more types may be used together. Moreover, it is not restricted only to the material mentioned above, Other materials may be used.

  The thickness of the solid polymer electrolyte membrane may be appropriately determined in consideration of the characteristics of the obtained fuel cell, and is not particularly limited. The thickness of the electrolyte membrane is usually about 5 to 100 μm. When the thickness of the electrolyte membrane is within such a range, the balance of strength during film formation, durability during use, and output characteristics during use can be appropriately controlled.

[Production method of membrane electrode assembly]
A method for producing the membrane electrode assembly is not particularly limited, and a conventionally known method can be used. For example, a catalyst layer is transferred or applied to a solid polymer electrolyte membrane by hot pressing and dried, and a gas diffusion layer is bonded to the dried layer, or a catalyst layer is applied in advance to the porous layer surface of the gas diffusion layer and dried. By doing so, two gas diffusion electrodes (GDE) can be produced, and this gas diffusion electrode can be joined to both surfaces of the solid polymer electrolyte membrane by hot pressing. Application and joining conditions such as hot pressing may be appropriately adjusted according to the type of polymer electrolyte in the solid polymer electrolyte membrane or catalyst layer (perfluorosulfonic acid type or hydrocarbon type).

[Separator]
The separator has a function of electrically connecting each cell in series when a plurality of single cells of a fuel cell such as a polymer electrolyte fuel cell are connected in series to form a fuel cell stack. The separator also functions as a partition that separates the fuel gas, the oxidant gas, and the coolant from each other. In order to secure these flow paths, as described above, each of the separators is preferably provided with a gas flow path and a cooling flow path. As a material constituting the separator, conventionally known materials such as dense carbon graphite, carbon such as a carbon plate, and metal such as stainless steel can be appropriately employed without limitation. The thickness and size of the separator and the shape and size of each flow path provided are not particularly limited, and can be appropriately determined in consideration of the desired output characteristics of the obtained fuel cell.

  The type of the fuel cell is not particularly limited. In the above description, the polymer electrolyte fuel cell (PEFC) has been described as an example. However, in addition to the above, an alkaline fuel cell and a direct methanol fuel cell are used. And a micro fuel cell. Among them, a polymer electrolyte fuel cell is preferable because it is small in size, and can achieve high density and high output. The fuel cell is useful as a power source for stationary vehicles as well as a power source for a moving body such as a vehicle in which a mounting space is limited. Particularly, the fuel cell is particularly useful for an automobile application in which system start / stop and output fluctuation frequently occur. It can be suitably used.

  The manufacturing method of the fuel cell is not particularly limited, and conventionally known knowledge can be appropriately referred to in the field of the fuel cell.

  The fuel used when operating the fuel cell is not particularly limited. For example, hydrogen, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, secondary butanol, tertiary butanol, dimethyl ether, diethyl ether, ethylene glycol, diethylene glycol and the like can be used. Of these, hydrogen and methanol are preferably used in that high output is possible.

  Furthermore, a fuel cell stack having a structure in which a plurality of membrane electrode assemblies are stacked and connected in series via a separator may be formed so that the fuel cell can exhibit a desired voltage. The shape of the fuel cell is not particularly limited, and may be determined as appropriate so that desired battery characteristics such as voltage can be obtained.

  The PEFC and membrane electrode assembly described above use a member that can achieve both dryout resistance and flooding resistance. Therefore, the PEFC and the membrane electrode assembly exhibit excellent power generation performance that is not easily affected by fluctuations in humidity.

  The effects of the present invention will be described using the following examples and comparative examples. However, the technical scope of the present invention is not limited only to the following examples. In the following examples, the operation was performed at room temperature (25 ° C.) unless otherwise specified. Unless otherwise specified, “%” and “part” mean “% by weight” and “part by weight”, respectively.

Example 1
2 g of styrene block polymer (polystyrene-poly (ethylene-ethylene / propylene) block-polystyrene SEPTON (registered trademark) SEEPS4055, manufactured by Kuraray Co., Ltd.) was added to 40 g of toluene. The mixture was stirred at 600 rpm for 15 minutes while being heated to 80 ° C. to obtain a polymer solution (1) (resin solid content concentration: 5% by weight). The styrene block polymer used in this example has a surface contact angle (water repellency) to water of 101.2 ° and a solubility in toluene (30 ° C.) of 10% by weight or more.

In the polymer solution (1) thus obtained, 1.75 times (weight) (3.5 g) of the styrene block polymer and 0.25 times (weight) of the acetylene black and styrene block polymer. ) (0.5 g) of graphite was added and mixed to obtain a mixture. As acetylene black, Denka Black AB6 (manufactured by Denki Kagaku Kogyo, primary average particle size: 40 nm, BET specific surface area: 37 m ² / g) was used. Moreover, SP-20 (made of Japanese graphite, scaly, BET specific surface area: 6 m ² / g, average long side: 16.8 μm, average short side: 0.63 μm) was used as graphite.

  Next, after the above mixture was stirred for 4 minutes by setting the revolution / spinning speed at 450 rpm in a self-revolving stirring deaerator mixer (manufactured by EME, model: UFO-3), the revolution / spinning speed was respectively set. The ink was obtained by stirring for 8 minutes at 900 rpm and 450 rpm. The obtained ink was pulverized for 3 minutes at 13500 revolutions / minute with a homogenizer (manufactured by IKA, ULTRA-TURREX T25) to obtain an ink composition (1). In the ink composition (1), acetylene black was present as an aggregate having an average secondary particle size of about 1.7 μm.

Next, this ink composition (1) was applied (blade coating) on carbon paper (thickness: 190 μm, pore diameter: 126.7 μm, surface contact angle 129.9 °) with an applicator. After coating, the carbon paper is naturally dried at room temperature (25 ° C.) for 20 minutes to form a porous layer having a film thickness (dry film thickness) of 60 μm on the carbon paper, resulting in a gas diffusion layer having a total thickness of 220 μm. (1) was obtained.
As carbon paper, model number: 25BA (hydrophobized with 5 wt% PTFE) (thickness: 190 μm) manufactured by SGL was used. Moreover, when the hole diameter of this carbon paper was measured, it was 126.7 micrometers.

  The cross section of the gas diffusion layer (1) thus obtained was observed with a scanning electron microscope (SEM), and the result is shown in FIG. 3A. Further, the surface of the gas diffusion layer (1) was observed with an optical microscope (25 times), and the result is shown in FIG. 3B. As shown in FIG. 3A, a porous layer (“4” portion in FIG. 3A) having a film thickness (dry film thickness) of 60 μm is on carbon paper (porous substrate) (“2” portion in FIG. 3A). Are observed to form. In addition, a porous layer is also formed in the vicinity of the surface layer of carbon paper (porous substrate) (thickness portion of about 30 μm from the surface: a portion obtained by subtracting “1” from “2” in FIG. 3A). Is observed. For this reason, the gas diffusion layer (1) has a total thickness of 90 μm (portion “3” in FIG. 3A), but the gas diffusion layer (1) has a total thickness of 220 μm. Further, from FIG. 3B, it is observed that the porous layer forming surface (application surface in FIG. 3B) of the gas diffusion layer (1) has a smooth surface and there is no defective application portion. This is considered that graphite and acetylene black are uniformly laminated on carbon paper, so that the surface of the gas diffusion layer can maintain smoothness. FIG. 3B also shows that in the gas diffusion layer (1) of the present invention, no mixture is observed on the porous substrate side (the back surface in FIG. 3B) (corresponding to the result of 3A above).

  Further, when the surface contact angle (water repellency) of the gas diffusion layer (1) thus obtained with respect to water was measured, the surface contact angle on the side where the porous layer was formed was 132.0 °, and the porous layer The surface contact angle on the side where no is formed was 130.0 °. From this result, it is considered that the gas diffusion layer of the present invention can exhibit sufficient water repellency.

Example 2
In Example 1, carbon paper (model number manufactured by SGL: 25AA (non-hydrophobized) (thickness: 190 μm) was used in the same manner as Example 1 except that it was used instead as a porous substrate. A gas diffusion layer (2) was produced, and the surface contact angle of the carbon paper used in this example could not be measured because water penetrated (surface contact angle = less than 90 °). When the pore diameter of the carbon paper was measured, it was 126.7 μm.

  When the cross section of the gas diffusion layer (2) thus obtained was observed with a scanning electron microscope (SEM), a porous layer having a film thickness (dry film thickness) of 30 μm was found on the carbon paper (porous substrate). Was formed. Moreover, it is observed that the porous layer is formed also in the surface layer vicinity part (thickness part of about 60 micrometers from the surface) of carbon paper (porous base material). Therefore, the gas diffusion layer (2) has a total porous layer thickness of 90 μm, but the gas diffusion layer (2) has a total thickness of 220 μm. It is also observed that the surface of the gas diffusion layer (2) (coating film) is smooth. This is considered that graphite and acetylene black are uniformly laminated on carbon paper, so that the surface of the gas diffusion layer can maintain smoothness.

  The surface of the gas diffusion layer (2) thus obtained was observed with an optical microscope (100 times), and the results are shown in FIG. As shown in FIG. 4, the porous layer forming surface (application surface in FIG. 4) of the gas diffusion layer (2) has a smooth surface, and no exposure of carbon fibers constituting the porous substrate is observed. . Moreover, a poorly applied part is not observed on the porous layer forming surface (application surface in FIG. 4) of the gas diffusion layer (2). This is considered that graphite and acetylene black are uniformly laminated on carbon paper, so that the surface of the gas diffusion layer can maintain smoothness. Although not shown, when the cross section of the gas diffusion layer (2) was observed with an SEM, a porous layer with a film thickness (dry film thickness) of 60 μm was formed on the carbon paper and in the vicinity of the surface layer as in Example 1. It is observed that a porous layer was formed on each (thickness portion of about 30 μm from the surface). Therefore, the gas diffusion layer (2) has a total thickness of 90 μm, but the gas diffusion layer (2) has a total thickness of 220 μm.

  Further, when the surface contact angle (water repellency) of the gas diffusion layer (2) thus obtained with respect to water was measured, the surface contact angle on the side where the porous layer was formed was 131.4 °. The surface contact angle on the side where no is formed was 119.1 °. From this result, it is considered that the gas diffusion layer of the present invention can exhibit sufficient water repellency.

Comparative Example 1
As a reference comparative example, a commercially available member for gas diffusion layer (25BCH, manufactured by SGL, thickness 225 μm, fine) in which a microporous layer is formed on carbon paper (25BA) which is the same gas diffusion layer base material as in Example 1. Porous layer: 5 wt% PTFE-containing, microporous layer thickness of 35 μm) was used. This gas diffusion layer member is referred to as a gas diffusion layer (3). When the surface contact angle (water repellency) of this gas diffusion layer member (25BCH) with respect to water was measured, the surface contact angle on the side where the microporous layer was formed was 145.8 °, and the microporous layer was formed. The surface contact angle on the unfinished side was 135.0 °.

  For the gas diffusion layers (1) to (3) obtained in Examples 1 and 2 and Comparative Example 1, gas permeability and electrical resistance in the thickness direction were measured according to the following methods.

(Evaluation method)
1. Measurement of gas permeability in thickness direction Gurley Air Permeability Using Gurley Air Permeability Measurement as specified in JIS P8117: 2009, a clamping plate having a circular hole with an outer diameter of 28.6 mm is placed so that the porous layer surface is on the upper surface. The sample was fixed and the time required for 100 cc (0.1 dm ³ ) of air to pass through (permeation time (seconds)) was measured, and the Gurley air permeability [Permeability (unit: cc / cm ² / second)] was measured. Using this value, the gas permeability standardized by thickness [Permeability (unit: m ² )] was calculated. The results are shown in Table 1 below and FIG.

  From the above Table 1 and FIG. 5, it can be seen that the gas diffusion layers (1) and (2) of the present invention are significantly superior in gas diffusivity compared to the gas diffusion layer (3) of the comparative example. This is because scaly graphite covers a part of the pores on the surface of the carbon paper, and acetylene black penetrates in the entire thickness direction of the carbon paper to prevent the pores from being completely blocked. It is considered that the gas diffusion layer of the present invention can exhibit excellent gas diffusibility.

2. Measurement of electrical resistance in the thickness direction In measurement, both sides of a 0.95 cm ² test piece are sandwiched between gold foils, set in a penetration electrical resistance measurement device (TER-2000SS: ULVAC-RIKO), and a load is applied. Measured by energizing with The current value was 1 A, and 0.5 MPa to 5 MPa was taken as one cycle, and the values at 1 MPa in the second cycle were compared. The results are shown in Table 2 below and FIG.

  From Table 2 and FIG. 6, it can be seen that the gas diffusion layers (1) and (2) of the present invention have a lower resistance than the gas diffusion layer (3) of the comparative example. From this, it is considered that the gas diffusion layer of the present invention can exhibit excellent electrical conductivity.

  From Tables 1 and 2 and FIGS. 5 and 6, it is considered that the gas diffusion layers (1) and (2) of the present invention can exhibit high gas permeability while ensuring sufficient conductivity.

1 ... Polymer electrolyte fuel cell (PEFC),
2 ... Solid polymer electrolyte membrane,
3 ... Catalyst layer,
3a ... anode catalyst layer,
3c ... cathode catalyst layer,
4a ... anode gas diffusion layer,
4c ... cathode gas diffusion layer,
5a ... anode separator,
5c ... cathode separator,
6a ... anode gas flow path,
6c ... cathode gas flow path,
7: Refrigerant flow path,
10: Electrolyte membrane-electrode assembly (MEA),
20 ... porous substrate,
21 ... porous layer,
31 ... Specific shape graphite,
32 ... holes,
33 ... Other conductive substance.

Claims (6)

Mix the non-fluorinated elastomer resin, conductive material and oil-soluble solvent to prepare a mixture,
A non-fired gas diffusion layer comprising: applying the mixed liquid to a porous substrate; and drying to form a porous layer containing the non-fluorinated elastomer resin and a conductive material on the porous substrate. Production method.   The method according to claim 1, wherein the non-fluorinated elastomer resin has a surface contact angle with water of 100 ° or more and / or a solubility with respect to an organic solvent of 5% by weight or more.   The non-fluorinated elastomer resin is selected from the group consisting of hydrogenated petroleum resin, block copolymer of polystyrene and polyolefin, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, and acrylonitrile-butadiene-styrene copolymer. The method according to claim 2, which is at least one of the following.   4. The method according to claim 1, wherein the conductive substance includes at least one selected from the group consisting of rod-like graphite, needle-like graphite, plate-like graphite, columnar graphite, scale-like graphite, and spindle-like graphite. The method described.   The method according to claim 4, wherein the conductive material includes a conductive material having a long side length of 0.05 to 5 times a pore diameter of the porous substrate.   The method according to claim 1, wherein a surface contact angle of at least one surface of the non-fired gas diffusion layer with respect to water is 110 ° or more.