Gas diffusion electrode manufacturing method, gas diffusion electrode, and gas diffusion electrode roll

Abstract

To provide a method for manufacturing a gas diffusion electrode having uniform physical property related to a fine porous layer at low cost, and a gas diffusion electrode roll-like object having uniform physical properties related to the fine porous layer.SOLUTION: A method for manufacturing a gas diffusion electrode includes a step of coating a coating liquid containing conductive particles and a water-repellent resin onto a conductive porous base material, and feeds and coats the coating liquid from an agitation container to a coating device while agitating the coating liquid under the condition that vertical convection is generated in the coating liquid in the agitation container, wherein peripheral velocity of the outermost periphery of the agitation blade of the agitation device at this time is 0.8 m / s or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] Fuel cells are a mechanism for electrically extracting energy generated when hydrogen and oxygen react to produce water, and because they are highly energy efficient and produce only water as an exhaust, they are expected to become widespread as a clean energy source.The present invention relates to a gas diffusion electrode used in fuel cells, and in particular to a gas diffusion electrode used in a polymer electrolyte fuel cell, which is used as a power source for fuel cell vehicles and the like, and a method for manufacturing the same. [Background technology]

[0002] The electrodes used in polymer electrolyte fuel cells are sandwiched between two separators in polymer electrolyte fuel cells and are structured to consist of a catalyst layer formed on the surface of the polymer electrolyte membrane and a gas diffusion layer formed on the outside of this catalyst layer on both sides of the polymer electrolyte membrane. Gas diffusion electrodes are commonly used as individual components for forming the gas diffusion layer in electrodes. Performance requirements for gas diffusion electrodes include gas diffusivity, electrical conductivity for collecting electricity generated in the catalyst layer, and drainage properties for efficiently removing moisture generated on the surface of the catalyst layer. To obtain such gas diffusion electrodes, conductive porous substrates that combine gas diffusivity and electrical conductivity are used.

[0003] As the conductive porous substrate (hereinafter sometimes simply referred to as "substrate"), specifically, carbon felt, carbon paper, carbon cloth, and the like made of carbon fiber are preferably used, and among these, carbon paper is considered to be the most preferable in terms of mechanical strength, etc.

[0004] If the above-mentioned substrate is used as a gas diffusion electrode without modification, the coarseness of the fibers can easily cause large water droplets to form when water vapor condenses, resulting in flooding. For this reason, a microporous layer (also called a microporous layer) can be formed by applying a microporous layer coating (hereinafter simply referred to as "coating") containing dispersed conductive particles such as carbon black to a water-repellent substrate, followed by drying and sintering. The microporous layer provides a cosmetic effect by preventing the substrate's roughness from being transferred to the electrolyte membrane and by adequately filling the substrate's voids, thereby reducing the contact resistance (electrical resistance) between the catalyst layer and the gas diffusion layer. To achieve this cosmetic effect, the substrate's roughness (arithmetic mean roughness) is typically 10–30 μm, so the microporous layer thickness on the substrate (after drying and sintering) must be 10–80 μm, a large thickness for a wet coating. To ensure this thickness and to prevent the coating from soaking into the porous substrate, the coating must have a high viscosity. Furthermore, to improve the efficiency of power generation, there is a demand for fuel cells to be operated at temperatures of 90°C or higher. In such cases, it is particularly important to prevent a decrease in power generation performance due to drying up of the electrolyte membrane, and it is necessary to minimize the number of minute through-holes (pinholes) with a pore diameter of 2 to 10 μm.

[0005] On the other hand, in order for fuel cell vehicles to become widespread, it is important to reduce costs to the same level as gasoline vehicles. To achieve this, all costs, including material costs and processing costs, must be reduced, and gas diffusion layers are no exception.

[0006] As fuel cells and fuel cell vehicles become more widespread in the future, gas diffusion electrodes will also need to be made more suitable for mass production, with improved quality and cost reductions. Gas diffusion electrodes can be manufactured using either sheet-like manufacturing or continuous processing, but from the perspective of mass production, it is preferable to manufacture them continuously as long rolls of gas diffusion electrodes of 1,000 m or more, in which case physical properties such as in-plane gas diffusivity must be uniform over the entire length.

[0007] As a method for preparing a coating liquid for forming a microporous layer, Patent Document 1 discloses a technique for controlling shear force applied to conductive particles and a water-repellent resin (PTFE) to disperse and suppress aggregation. Patent Document 2 discloses a technique for improving the dispersibility of conductive particles by specifying the type of disperser. Patent Document 3 discloses a technique for improving drainage by leaving a prepared microporous layer coating liquid in a container to cause aggregation at the bottom of the container, generating cracks in the microporous layer. Patent Document 4 describes a method for controlling the size and number of the through holes. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 5148036 [Patent Document 2] Patent No. 4425364 [Patent Document 3] Patent No. 5922552 [Patent Document 4] Patent Publication No. 2018-156818 Summary of the Invention [Problem to be solved by the invention]

[0009] However, the microporous layer preparation methods described in Patent Documents 1 and 2 are insufficient to achieve high levels of quality, uniformity, and productivity for mass production of gas diffusion electrodes, and the technology of Patent Document 3 is also insufficient to ensure uniform quality and may even result in reduced productivity due to the additional step of aggregating the coating liquid. Furthermore, the level of control of the through pores in Patent Document 4 is insufficient to accommodate high-temperature operation of fuel cells.

[0010] An object of the present invention is to provide a gas diffusion electrode of uniform quality and to provide a technology for producing the gas diffusion electrode with high productivity and low cost. [Means for solving the problem]

[0011] In order to solve the above problems, the method for producing a gas diffusion electrode, the gas diffusion electrode, and the rolled gas diffusion electrode of the present invention have the following configurations. [1] A method for producing a gas diffusion electrode, comprising: a coating step of applying a microporous layer coating liquid containing conductive particles, a water-repellent resin, and a dispersion medium to a conductive porous substrate to form a microporous layer; a drying step of removing the dispersion medium from the microporous layer coating liquid; and a sintering step of sintering the microporous layer and the water-repellent resin of the conductive porous substrate, In the coating step, a microporous layer coating liquid stirring device having a container for stirring and an agitator comprising at least a stirring shaft and a stirring blade; a coater for applying the microporous layer coating liquid to the conductive porous substrate; A method for producing a gas diffusion electrode, comprising: using an agitator for a gas diffusion electrode having piping and a liquid delivery device for delivering the microporous layer coating liquid from the microporous layer coating liquid agitator to a coater; delivering the microporous layer coating liquid by the liquid delivery device and applying the coating liquid while stirring the microporous layer coating liquid with the agitator under conditions that generate vertical convection in the microporous layer coating liquid in a container; and wherein the peripheral speed of the outermost periphery of the agitator blade during this process is 0.8 m / s or less. [2] The method for producing a gas diffusion electrode according to [1], wherein the microporous layer coating liquid is a water-based coating liquid. [3] The method for producing a gas diffusion electrode according to [1] or [2], wherein the viscosity of the microporous layer coating liquid is 1.0 Pa·s or more. [4] The method for producing a gas diffusion electrode according to any one of [1] to [3], wherein the microporous layer coating liquid has a shear thinning index (shear thinning index) defined in the specification of 1.5 or more. [5] The method for producing a gas diffusion electrode according to any one of [1] to [4], wherein the shape of the stirring blade is a helical ribbon blade or a paddle blade. [6] The method for producing a gas diffusion electrode according to any one of [1] to [5], wherein the rotation speed of the stirring blade is 20 rpm or less. [7] A gas diffusion electrode comprising a conductive porous substrate and a microporous layer for a gas diffusion layer containing conductive particles and a water-repellent resin, wherein the conductive particles contained in the microporous layer are carbon black, and through-holes penetrating the gas diffusion electrode from the surface of the microporous layer are 10 cm square (100 cm 2 ) and a maximum bubble point diameter of 2.0 μm or less. [8] The through-holes that penetrate from the surface of the microporous layer to the gas diffusion electrode are 10 cm square (100 cm 2 The gas diffusion electrode according to [7], characterized in that the number of bubbles per electrode is less than 2 and the maximum bubble point diameter is 1.0 μm or less. [9] The gas diffusion electrode according to [7] or [8], wherein the carbon black is acetylene black.

[10] A long rolled gas diffusion electrode comprising a conductive porous substrate and a microporous layer for a gas diffusion layer, the microporous layer containing conductive particles and a water-repellent resin, wherein the length of the rolled gas diffusion electrode is 1000 m or more and the relative standard deviation of in-plane gas diffusivity over the entire length is 5% or less. [Effects of the Invention]

[0012] The production method of the present invention makes it possible to obtain a gas diffusion electrode with no or very few through-pores, which is advantageous in terms of preventing dry-up during high-temperature operation, and it is possible to produce a gas diffusion electrode with a uniformly coated microporous layer with high production yield and efficiency, thereby reducing the production costs of the gas diffusion electrode and, ultimately, the fuel cell. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a schematic diagram of an example of an apparatus used to stir the coating liquid when applying the microporous layer coating liquid of the present invention. [Figure 2] 1 is a schematic diagram of an example of an apparatus for manufacturing a gas diffusion electrode of the present invention. [Figure 3] 1 is a schematic diagram showing the configuration of a gas diffusion electrode to which the present invention is applied; FIG. [Figure 4] 1 shows the shape of the stirring blade used in Comparative Example 2. [Figure 5] 1 is a diagram showing the properties of the coating liquid used in the present invention. [Figure 6] Schematic diagram of an in-plane gas diffusion evaluation device used in the examples of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] A first aspect of the present invention relates to a production method in which a microporous layer coating liquid having shear-thinning properties used in mass production of gas diffusion electrodes is applied to improve the uniformity of physical properties of the gas diffusion electrode after application and to increase the use efficiency of the coating liquid, by specifying a method for handling the coating liquid during application.

[0015] A second aspect of the present invention relates to a gas diffusion electrode comprising a conductive porous substrate and a microporous layer for gas diffusion containing conductive particles and a water-repellent resin, wherein the conductive particles are carbon black, the gas diffusion electrode has a small number of through-holes penetrating from the surface of the microporous layer through the gas diffusion electrode, and has a small maximum bubble point diameter.

[0016] The gas diffusion electrode produced by the production method of the first embodiment of the present invention and the gas diffusion electrode of the second embodiment have a microporous layer on at least one surface of a conductive porous substrate. First, the conductive porous substrate will be described.

[0017] In a polymer electrolyte fuel cell, the gas diffusion electrode must have high gas diffusivity to diffuse the gas supplied from the separator to the catalyst, high drainage to discharge water generated during the electrochemical reaction to the separator, and high conductivity to extract the generated current. For this reason, a conductive porous substrate made of a porous body having conductivity and a peak pore size in the range of 10 μm to 100 μm is used for the gas diffusion electrode.

[0018] Specific examples of the conductive porous substrate include porous substrates containing carbon fibers such as carbon fiber woven fabric, carbon fiber paper, carbon fiber nonwoven fabric, carbon felt, carbon paper, and carbon cloth, and metal porous substrates such as foamed sintered metal, metal mesh, and expanded metal. Among these, it is preferable to use a porous substrate containing carbon fibers because of its excellent corrosion resistance, and it is particularly preferable to use a substrate made by binding carbon fiber paper with a carbide, i.e., carbon paper, because of its excellent "springiness" that allows it to absorb dimensional changes in the thickness direction of the electrolyte membrane.

[0019] In order to improve the gas diffusion properties of the gas diffusion electrode and maximize the power generation performance of the fuel cell, the substrate must have a high porosity. The porosity is preferably 80% or more, and more preferably 85% or more. The upper limit of the porosity is 95%, which is the limit at which the substrate can maintain its structure.

[0020] Furthermore, the gas diffusion properties of the gas diffusion electrode can be improved by reducing the thickness of the substrate, such as carbon paper. Therefore, the thickness of the substrate, such as carbon paper, is preferably 220 μm or less, more preferably 150 μm or less, and even more preferably 120 μm or less. Setting the lower limit of the substrate thickness to 50 μm is preferable because it maintains mechanical strength and facilitates handling during the manufacturing process. Reducing the thickness of the conductive substrate is also effective in reducing the electrical resistance in the thickness direction when used in a fuel cell.

[0021] In order to efficiently produce a gas diffusion electrode using the above substrate, it is preferable to unwind a long roll of the substrate and form a microporous layer continuously during the time until the substrate is unwound.

[0022] The substrate may be subjected to a water-repellent treatment to improve drainage. The water-repellent treatment is preferably carried out using a water-repellent resin such as a fluororesin. Examples of fluororesins include polytetrafluoroethylene (PTFE) (such as Teflon (registered trademark)), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), perfluoroalkoxy fluoride resin (PFA), ethylene-tetrafluoroethylene copolymer (ETFA), polyvinylidene fluoride (PVDF), and polyvinyl fluoride (PVF). PTFE or FEP, which exhibit strong water repellency, are preferred.

[0023] The amount of the water-repellent resin is not particularly limited, but is preferably 0.1% by mass to 20% by mass relative to 100% by mass of the substrate. Within this range, water repellency is sufficiently exhibited, while the water-repellent resin is unlikely to clog pores that serve as gas diffusion paths or drainage paths, or to increase electrical resistance.

[0024] The method of treating a substrate for water repellency includes the commonly known treatment technique of immersing the substrate in a dispersion containing a water-repellent resin, as well as coating techniques of applying a water-repellent resin to the substrate by die coating, spray coating, etc. Dry processes such as sputtering of fluororesin can also be applied. After the water-repellent treatment, a drying step and even a sintering step may be added as needed.

[0025] Next, the microporous layer will be described. The microporous layer is a layer containing conductive particles such as carbon black, carbon nanotubes, carbon nanofibers, chopped carbon fibers, graphene, and graphite. Carbon black is preferably used as the conductive particles from the viewpoints of low cost, safety, and stability of product quality. Acetylene black is preferably used as the carbon black contained in the microporous layer because it contains few impurities and is less likely to reduce the activity of the catalyst.

[0026] Furthermore, the microporous layer is required to have properties such as electrical conductivity, gas diffusion, water drainage or moisture retention, and thermal conductivity, as well as strong acid resistance on the anode side and oxidation resistance on the cathode side inside the fuel cell, and therefore contains a water-repellent resin such as a fluororesin in addition to the conductive particles. Examples of the fluororesin contained in the microporous layer include PTFE, FEP, PFA, ETFA, etc., similar to fluororesins preferably used to make substrates water-repellent. PTFE or FEP is preferred because of its particularly high water repellency.

[0027] For a gas diffusion electrode to have a microporous layer, a coating liquid for forming the microporous layer, i.e., a microporous layer coating liquid, is generally applied to a substrate. The coating liquid typically contains the above-mentioned conductive particles and a dispersant such as water or alcohol. However, from the viewpoints of reducing environmental impact and simplifying the coating and drying process, an aqueous coating liquid using water as the dispersant is preferred. Here, an aqueous coating liquid refers to a coating liquid in which water accounts for 50% by weight or more of the dispersant, preferably 70% by weight or more, and more preferably 90% or more. Furthermore, a surfactant or the like is often blended as a dispersant for dispersing the conductive particles. Furthermore, the coating liquid used in the present invention is pre-loaded with a water-repellent resin in order to incorporate the water-repellent resin into the microporous layer.

[0028] To prepare the microporous layer coating liquid, various dispersing machines and kneading machines can be used, such as a planetary mixer, ball mill, bead mill, jet mill, kneader, pressure kneader, continuous kneader, homogenizer, and homomixer. Furthermore, when preparing an aqueous coating liquid containing a surfactant as a dispersant, foaming is likely to occur, so an apparatus that does not incorporate air or that can perform preparation while vacuum degassing is preferred. From this viewpoint, a multi-screw kneader such as a planetary mixer is suitable.

[0029] A preferred method for forming a microporous layer on a substrate is to apply a coating liquid to the substrate.

[0030] From the viewpoint of productivity of the coating liquid, the concentration of the conductive particles in the coating liquid is preferably 5% by mass or more, more preferably 10% by mass or more. There is no upper limit to the concentration as long as the viscosity, dispersion stability of the conductive particles, coatability of the coating liquid, etc. are suitable. When acetylene black is used as the conductive particles, in the case of an aqueous coating liquid, the upper limit of the acetylene black concentration in the coating liquid is preferably 25% by mass. Within this preferred range, the acetylene black particles do not re-aggregate, causing so-called percolation, and there is little possibility that the coatability of the coating liquid will be impaired due to a sudden increase in viscosity.

[0031] The roles of the microporous layer are (1) protecting the catalyst, (2) providing a cosmetic effect by preventing the surface of the coarse substrate from being transferred to the electrolyte membrane, and (3) preventing condensation of water vapor generated at the cathode. Of the above, in order to achieve the cosmetic effect, it is preferable that the microporous layer has a certain thickness.

[0032] The thickness of the microporous layer is preferably 10 μm or more and 60 μm or less. If the thickness of the microporous layer is less than 10 μm, the above-mentioned touch-up effect may be insufficient. To fully exert the touch-up effect, a thickness of 20 μm or more is preferable. Furthermore, if the thickness of the microporous layer exceeds 60 μm, the gas diffusion property of the gas diffusion electrode itself may decrease or the electrical resistance may increase. From the viewpoint of improving gas diffusion property or reducing electrical resistance, the thickness of the microporous layer is more preferably 50 μm or less, and even more preferably 40 μm or less. Note that, since the microporous layer is formed by applying a coating liquid to the surface of the substrate, the coating liquid may penetrate into the pores of the substrate, forming a permeated portion 203 of the microporous layer in the substrate as shown in FIG. 3. The thickness of each microporous layer refers to the thickness of the portion outside the substrate, excluding this permeated portion.

[0033] In the present invention, as described above, it is preferable to thickly coat a microporous layer on a substrate with high porosity. In order to coat a coating liquid thickly without soaking it into a substrate with high porosity as much as possible, it is preferable that the viscosity is low at the moment of application when shear force is applied, and high when the dispersion medium is dried. In other words, it is preferable that the coating liquid has shear thinning properties. Shear thinning properties are the property of temporarily decreasing viscosity when shear force is applied (and recovering viscosity when the shear force is removed).

[0034] In the microporous layer coating liquid used in the present invention, a quantitative index of shear thinning property (hereinafter referred to as the shear thinning index) is defined as the ratio (a / b) of the viscosity value (a) at a shear rate (shear rate) of 17 ( / s) to the viscosity value (b) at a shear rate of 127 ( / s). A high shear thinning index indicates high viscosity when no shear force is applied and low viscosity when high shear force is applied. In the microporous layer coating liquid used in the present invention, this shear thinning index is preferably 1.5 or more, more preferably 2.0 or more. The upper limit of the shear thinning index is preferably 10.0 or less, more preferably 8.0 or less.

[0035] The coating liquid is prepared by dispersing conductive particles in a dispersion medium. To disperse the conductive particles, it is preferable to use a surfactant as a dispersant. To stabilize this dispersion for a long period of time and prevent the coating liquid from separating, the amount of dispersant added is preferably 10% by mass or more of the conductive particles in the coating liquid. If the amount is less than 10% by mass, the dispersion stability of the coating liquid cannot be ensured, and changes such as a decrease in the physical properties of the coating liquid are likely to occur. Furthermore, when a water-repellent resin is used, it is preferable to use a dispersant that does not interfere with the dispersion of the water-repellent resin.

[0036] Furthermore, if the thickness of the microporous layer is to be greater than 10 μm as a coating film after sintering, the viscosity of the coating liquid is preferably 1.0 Pa·s or more, more preferably 3.0 Pa·s or more, and even more preferably 5.0 Pa·s or more. If the viscosity of the coating liquid is less than 1.0 Pa·s, the coating liquid may flow on the surface of the substrate, making it impossible to achieve the desired thickness, or the coating liquid may flow into the pores of the substrate, causing bleed-through. Conversely, if the viscosity of the coating liquid is too high, the coatability may be reduced, so the viscosity of the coating liquid is preferably 25 Pa·s or less, more preferably 20 Pa·s or less, and even more preferably 15 Pa·s or less.

[0037] Adding a thickener is effective in maintaining a high viscosity of the coating liquid. The thickener used here may be a commonly known thickener. For example, methyl cellulose-based, polyethylene glycol-based, polyvinyl alcohol-based, etc. are preferably used.

[0038] These dispersants and thickeners may be a single substance that functions as both a dispersant and a thickener, or may have other functions, such as antifungal properties. Surfactants are preferred as substances that function as both dispersants and thickeners. Alternatively, different substances suitable for each function may be selected as the dispersant and thickener. In this case, it is preferable to select a thickener that does not interfere with the dispersion of the conductive particles or water-repellent resin. To maintain the viscosity and dispersion stability of the coating liquid, the total amount of dispersant and thickener is preferably 10% by mass or more of the added mass of conductive particles, more preferably 50% by mass or more, and even more preferably 100% by mass or more. The preferred upper limit of the total amount of dispersant and thickener is usually 500% by mass or less of the added mass of conductive particles. At 500% by mass or less, steam and decomposition gases are less likely to be generated during the subsequent sintering process, ensuring safety and productivity.

[0039] The coating liquid can be dispersed using various dispersing devices, but excessive dispersion often results in a decrease in viscosity, and even if the viscosity is adjusted with a thickener, the coating liquid tends to penetrate into the porous substrate. Therefore, it may be necessary to keep the dispersion at a low level and maintain it. In other words, after preparing the coating liquid, it is preferable to avoid applying shear forces that would change the dispersion state of the conductive particles as much as possible until the coating liquid is applied to the substrate.

[0040] The above-mentioned coating liquid, particularly when the dispersion medium is aqueous and a surfactant is added as a dispersant or thickener, is prone to generating bubbles during operations such as stirring. When a coating liquid containing bubbles is applied to a substrate, a coating film is not formed in the areas where the bubbles exist, resulting in a phenomenon known as coating voids, which may reduce the functionality of the microporous layer. Therefore, the coating liquid must be thoroughly degassed before application.

[0041] The gas diffusion electrode manufacturing apparatus of the present invention includes at least a microporous layer coating liquid agitator having a container and agitator for preparing the microporous layer coating liquid, a coater for applying a microporous layer to a substrate, and piping and a liquid feeder for feeding the microporous layer coating liquid from the microporous layer agitator to the coater, and the coating liquid is applied to the substrate by the coater to produce a gas diffusion electrode.

[0042] As mentioned above, it is preferable to avoid generating bubbles in the coating liquid during transfer from the container to the coater or during coating, as this can cause coating defects. Stirring in the container may be stopped to prevent bubbles from forming. However, stopping for long periods of time, in particular, can cause a distribution in the density or viscosity of the coating liquid within the container. That is, the closer to the bottom of the container, the higher the density and viscosity of the coating liquid tend to be. When a long-length gas diffusion electrode is coated in a state where a distribution has occurred, even if the coating amount per hour is set to achieve the target coating liquid basis weight and thickness based on the coating liquid with high density and viscosity near the bottom of the container at the start of coating, as coating progresses, a coating liquid with a lower density and viscosity than the coating liquid at the top of the container will be coated. If coating is continued at the same volumetric rate, the basis weight will decrease and the viscosity will decrease, making it easier to penetrate, which tends to reduce the thickness of the gas diffusion electrode. This tendency is particularly noticeable when large volumes of coating liquid are continuously coated in mass production. That is, when continuously producing gas diffusion electrodes by long-length coating, it is important to make the composition of the coating liquid uniform in the container in which the coating liquid is prepared and to prevent bubbles from being generated in the coating liquid.

[0043] Furthermore, the microporous layer coating liquid used in the present invention preferably has a high viscosity. However, when a highly viscous coating liquid is extracted from an extraction port at the bottom of a large-capacity container using a pump or the like, once the liquid level drops to a certain level, the liquid flows only in the region directly above the extraction port, and as shown in Figure 5, the phenomenon of the coating liquid near the wall surface not being transported is likely to occur, resulting in a decrease in the usage rate of the microporous layer coating liquid.

[0044] As a result of investigations aimed at solving these problems, the present inventors have found that, when the coating liquid is fed to the coater, the composition of the coating liquid in the container is kept uniform to the end by operating the agitator so as to generate vertical convection in the coating liquid in the container, thereby making it possible to make the physical properties of the microporous layer of a long gas diffusion electrode uniform from start to finish and to increase the utilization efficiency of the coating liquid in the container.

[0045] An example of the method for producing a gas diffusion electrode according to the first embodiment of the present invention will now be described in detail, but the present invention is not limited to the following description.

[0046] In the microporous layer coating liquid stirring device of the present invention, as illustrated in Fig. 1, a coating liquid 4 is placed in a vessel 1 equipped with an agitator 2 having an agitating blade 21 and an agitating shaft 22, and is stirred by the agitating blade 21. The vessel 1 is connected to a pressure reducing means (not shown) via a pressure reducing means connection port 3, and the internal pressure of the vessel 1 is controlled by the pressure reducing means, such as a vacuum pump. A baffle plate may be provided in the vessel 1 to adjust the agitation state of the coating liquid.

[0047] The container is constructed to be sealable, and its internal pressure is controlled by a pressure reducing means during degassing. The container capacity is not particularly limited, but when applied to mass production, it is preferably 200 liters or more, more preferably 300 liters or more, and even more preferably 1000 liters or more. Considering the installation space and the efficiency of temperature control from the outside, the upper limit of the capacity is thought to be about 3000 liters.

[0048] The shape of the container can be, for example, a tank having a cylindrical straight body and a mirror-shaped bottom, but in order to use as much of the coating liquid as possible, it is preferable that the bottom be bowl-shaped. There is no limitation on the shape of the top of the container, and a flat or mirror-shaped top can be used. There is no limitation on the top having a lid-like structure, and it can be openable, closable, or removable. There is also no particular limitation on the material of the container, and it can be freely selected depending on the properties of the coating liquid.

[0049] The container preferably has a pressure reducing means connection port for connecting to pressure reducing means. By connecting the pressure reducing means connection port to pressure reducing means (e.g., a vacuum pump), the pressure inside the container can be reduced to a pressure below atmospheric pressure. There are no limitations on the size or shape of the pressure reducing means connection port. Furthermore, the pressure reducing means is not limited to a vacuum pump, and any known device that can control the pressure inside the container can be used.

[0050] The container is provided with an outlet for sending the coating liquid to the coating device. A coating liquid supply section may also be provided. A separate gas supply connection port may also be provided for supplying gas when returning the pressure from a reduced pressure state to atmospheric pressure. If temperature control of the coating liquid is required, the temperature can be controlled by immersing a coiled heat transfer medium pipe in the coating liquid, or by giving the container a jacket structure and running a heat transfer medium through this jacket, or by attaching a heater to the side of the container, or by other means.

[0051] The coating liquid used in the present invention may have physical properties such as viscosity that are highly temperature-dependent. In such cases, it is preferable to control the temperature of the coating liquid constant from the degassing process to the transfer of the coating liquid to the coating device, and from the moment the coating liquid is discharged from the coater and applied to the substrate. It is also desirable to maintain the same temperature in the coating liquid disperser, the transfer section from the disperser to the stirring vessel, and even the building section in which these devices are installed. The temperature fluctuation range is ±5°C from the center value, preferably ±3°C, and more preferably ±1°C. The more constant the temperature control, the better in terms of uniforming the liquid physical properties. However, since the control mechanism becomes expensive, the practical limit is about ±1°C.

[0052] The coating liquid in the container is stirred by a stirrer. The container is preferably equipped with a stirring blade, which is a component of the stirring mechanism. The stirrer is not particularly limited as long as it can generate vertical convection in the highly viscous and shear-thinning coating liquid inside and uniformly stir the inside, and any known stirring device can be used. For example, a stirring mechanism with stirring blades such as paddle blades or turbine blades fixed to the stirring shaft can be used. The stirring blades may be provided in one stage on the stirring shaft, or in two or more stages. However, for the coating liquid used in the present invention, stirring blades known as helical ribbon blades are preferably used. Furthermore, stirring blades commonly known as paddle blades, such as "Maxblend®" blades (Sumitomo Heavy Industries Process Equipment Co., Ltd.) and "Fullzone®" blades (Kobe Eco-Solutions Co., Ltd.), may also be used because of their simple structure, which allows for easy cleaning when switching product types.

[0053] The position of the stirring mechanism within the container is not particularly limited as long as it can stir the coating liquid. The material of the stirring mechanism is also not particularly limited and can be appropriately selected depending on the properties of the coating liquid.

[0054] The occurrence of vertical convection can be confirmed, for example, by placing beads having an apparent density equivalent to that of the coating liquid in the liquid and visually observing the movement of the beads when the liquid is stirred. If vertical convection is occurring, beads that have fallen to the liquid surface will sink with the current that is directed toward the bottom of the container due to stirring, and then reappear on the liquid surface with the current that is rising, and this process is repeated. If vertical convection is not occurring, the beads will continue to float near the liquid surface, or will sink and not rise to the liquid surface. The beads used here should have a density approximately equivalent to that of the coating liquid (preferably the density of the liquid ±0.1 g / cm). 3 ) that is insoluble in the coating liquid.

[0055] A baffle plate may also be provided in the vessel. There are no particular limitations on the shape of the baffle plate, and any known shape such as a flat plate or a cylindrical shape may be used.

[0056] The coating liquid in the stirring device is extracted from an outlet near the bottom of the container and delivered to the coater using a pump or other means for generating a pressure differential from upstream to downstream. If necessary, the container may be pressurized to deliver the coating liquid. During delivery, operating the stirring blades at a rotation speed or peripheral speed that does not generate bubbles or entrain bubbles into the coating liquid is preferred, as this generates vertical convection within the container and maintains uniform composition and physical properties within the container. The generation of bubbles can be investigated, for example, by the following method: Two 15 cm x 0.5 cm thick glass plates are prepared. Fluorine tape (ASF-110FR, manufactured by Chukoh Chemical Industry Co., Ltd.) is attached to the four corners of one plate, and a 0.2 g liquid sample is sandwiched between them and allowed to stand for 30 minutes. The sample is then observed using an ILLMINATED MAGNIFIERS OSL-1 manufactured by Otsuka Optical Co., Ltd., and photographed with a digital camera or other device. The number of bubbles in the image can be visually counted to determine the presence or absence of bubbles.

[0057] The rotation speed of the impeller depends on the viscosity and other physical properties of the coating liquid. However, a rotation speed that results in a peripheral speed of the outermost periphery of the impeller (impeller tip speed) of 0.8 m / s or less prevents the generation of bubbles and maintains nearly uniform coating liquid properties. Because the coating liquid used in the present invention exhibits shear-thinning properties, high-speed rotation can reduce viscosity due to shear with the container wall or bottom. If the coating liquid is applied at this viscosity, it may penetrate more deeply into highly porous substrates. Therefore, a lower impeller tip speed is preferred, with 0.5 m / s or less, and even 0.1 m / s or less, being preferable. The lower limit of the impeller tip speed is not particularly limited as long as it generates movement in the impeller and generates vertical convection. However, from the perspective of stable operation of the stirring mechanism, it is preferable to set it to 0.01 m / s or more. Here, the impeller tip speed can be calculated using the impeller diameter (m) and the agitator rotation speed (rpm) using the following formula: Impeller tip speed (m / s) = Mixer rotation speed (rpm) / 60 × impeller diameter (m) × pi Here, the diameter of the stirring blade is the diameter of the blade when the plane parallel to the liquid surface is circular, and if it is not circular, it is the diameter of the circumscribed circle of the path that the blade traces when rotating.

[0058] Furthermore, even if the peripheral speed of the outermost periphery of the stirring blade is 0.8 m / s or less, if the blade diameter is small and there is a possibility of air bubble entrapment, it is advisable to reduce the rotation speed, preferably 20 rpm or less, and even more preferably 15 rpm or less.

[0059] The delivered coating solution can be applied to the substrate using various commercially available coating devices. Examples of coating methods that can be used include screen printing, rotary screen printing, spraying, intaglio printing, gravure printing, die coater coating, bar coating, blade coating, and roll knife coater coating. However, die coater coating is preferred because it allows for quantification of the coating amount regardless of the surface roughness of the substrate. Furthermore, blade coaters and roll knife coaters are preferred when a smooth coating surface is required to enhance adhesion with the catalyst layer when the gas diffusion electrode is incorporated into a fuel cell. The coating methods listed above are merely examples and are not necessarily limited to these. The various coating methods listed above are described in numerous existing publications, such as "All About Converting" (edited by the Processing Technology Research Association, March 2014).

[0060] After the coating liquid is applied, the dispersion medium of the coating liquid is dried and removed as necessary. When the dispersion medium is water, the drying temperature after application is preferably 20°C or higher and 150°C or lower, and more preferably 60°C or higher and 140°C or lower. The drying temperature may be within a range that combines any of the upper and lower limits above. This drying of the dispersion medium may be performed all at once in the subsequent sintering step.

[0061] After the coating liquid is applied, sintering is generally carried out in order to remove the dispersant and thickener used in the coating liquid and to dissolve the water-repellent resin once to bind the conductive particles.

[0062] The sintering temperature depends on the boiling point or decomposition temperature of the added dispersant and thickener, but is preferably 250° C. or higher and 400° C. or lower. More preferably, it is 300° C. or higher and 380° C. or lower. When the sintering temperature is in this preferred range, the dispersant and thickener can be sufficiently removed, while the possibility of decomposition of the water-repellent resin is low.

[0063] Once sintering is complete, the gas diffusion electrode is wound onto a winding core by a winding machine. The core material used for winding can be a paper tube, plastic, metal, or other material. The outer diameter of the core should be in the range of 80 mm to 180 mm, as a too small diameter can cause cracking of the substrate, while a too large diameter can reduce handling. During winding, a paper insert can be wound around the gas diffusion electrode to protect its surface.

[0064] Next, the characteristics of the gas diffusion electrode according to the second embodiment will be described. The gas diffusion electrode of the present invention has a microporous layer for gas diffusion, which contains conductive particles and a water-repellent resin, on at least one surface of a conductive porous substrate. A preferred method for producing the gas diffusion electrode according to the second embodiment of the present invention is the production method according to the first embodiment of the present invention.

[0065] The gas diffusion electrode of the second embodiment of the present invention has the characteristic of having few through-holes. Normally, a microporous layer has countless fine pores with a diameter of less than 1.0 μm, which contribute to gas diffusion in the direction perpendicular to the surface. However, if the diameter specifically exceeds 2.0 μm and the pores become through-holes, when an electrode (catalyst layer) is formed by the so-called GDE method in which a catalyst ink is applied to the microporous layer side of the gas diffusion electrode, the catalyst ink may flow out of the through-holes, potentially reducing the catalyst's contribution to power generation. Furthermore, during power generation at high temperatures, water vapor may leak out of the through-holes, potentially causing so-called dry-up. In the gas diffusion electrode of the second embodiment of the present invention, the through-holes are arranged in an area of ​​10 cm square (100 cm 2 If there are five or more through holes, the power generation performance at high temperatures may decrease. The number of through holes is preferably less than two, and more preferably less than one.

[0066] To check the number of through-holes in the gas diffusion electrode, an optical microscope (stereomicroscope) is used, and with the microporous layer of the gas diffusion electrode facing up, light is shone from below, and the parts through which the light passes are counted as through-holes.

[0067] The diameter of the through-holes can also be determined by the bubble point method. The pore diameter measured by the bubble point method is called the bubble point diameter (hereinafter, sometimes called the BP diameter). The measurement method and the like will be described later. In the second aspect of the present invention, the maximum bubble point diameter is 2.0 μm or less, preferably 1.0 μm or less, and more preferably 0.5 μm or less.

[0068] The porosity of the microporous layer is preferably less than 80% to prevent dry-up at high temperatures. However, if the porosity is too low, gas diffusion properties are impaired, so the lower limit is 60%. When such a gas diffusion electrode is incorporated into a fuel cell, dry-up can be suppressed and power generation performance at high temperatures can be improved.

[0069] Next, a rolled gas diffusion electrode according to a third embodiment of the present invention will be described.

[0070] A third aspect of the present invention is a roll-shaped product suitable for mass production of gas diffusion electrodes, characterized in that the variation (relative standard deviation) of in-plane gas diffusivity over the entire length is within 5%. A preferred method for producing the roll-shaped gas diffusion electrode of the third aspect is the production method of the first aspect.

[0071] For mass production of gas diffusion electrodes, a long roll is preferred, and the length of the effective portion of the rolled gas diffusion electrode of the present invention must be 1000 m or more, preferably 3000 m or more, and more preferably 5000 m or more. Since the thickness of the gas diffusion electrode is at most about 60 μm, the upper limit of the length is about 100,000 m from the viewpoint of handleability.

[0072] The most basic characteristics of a gas diffusion electrode are its thickness and the basis weight of the microporous layer, which can be set to any value as a design parameter for the fuel cell, but if the thickness and basis weight of the microporous layer are not uniform, problems such as uneven clamping pressure when the electrode is incorporated into a fuel cell may occur. Therefore, it is preferable that the variation (relative standard deviation) in the thickness and basis weight of the microporous layer be within 5%.

[0073] If the physical properties (viscosity) of the microporous layer coating liquid are not uniform, when attempting to maintain a constant basis weight of the microporous layer, the degree of penetration of the microporous layer coating liquid into the highly porosity conductive porous substrate will vary, making it difficult to maintain a constant thickness at the same basis weight. The in-plane gas diffusivity of the gas diffusion electrode is an indicator of the degree of this penetration, and the variation in in-plane gas diffusivity needs to be kept within 5%, preferably within 3%. To achieve such uniformity of physical properties over the entire length of the roll, it is preferable to apply the production method of the first aspect when applying the microporous layer coating liquid, i.e., to generate vertical convection in the coating liquid while stirring and then send it to the coater. [Example]

[0074] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0075] (a) Conductive porous base material Thickness 100μm, width 550mm, length 5000m, porosity 85%, density 0.25g / cm 3 Carbon paper was prepared and subjected to a water-repellent treatment in advance using a die coater with a diluted solution of PTFE dispersion ("Polyflon (registered trademark)" D-210C, manufactured by Daikin Industries, Ltd.) and the dispersion medium was dried off.

[0076] (b) Preparation of coating solution Ten parts by mass of Denka Black (registered trademark) manufactured by Denki Kagaku Kogyo Co., Ltd., 6 parts by mass of a PTFE dispersion (Polyflon (registered trademark) D-210C manufactured by Daikin Industries, Ltd.), 10 parts by mass of a surfactant (TRITON (registered trademark) X-100 manufactured by Nacalai Tesque, Inc.), and 74 parts by mass of ion-exchanged water were kneaded in a planetary mixer to a working volume of 200 liters.

[0077] (c) Viscosity measurement In the viscosity measurement mode of a Spectris Bohlin rotational rheometer, a circular cone plate with a diameter of 40 mm and a 2° inclination was used, and stress was measured while increasing the plate rotation speed (while increasing the shear rate). At this time, the viscosity value a at a shear rate of 17 (1 / s) was read and used as the viscosity of the coating liquid. The viscosity value b at a shear rate of 127 (1 / s) was also measured, and the ratio a / b was used as the shear thinning index.

[0078] The viscosity of the coating liquids used in the examples and comparative examples was 8.8 to 9.8 Pa·s, and the shear thinning index (a / b) was within the range of 4.3 to 4.5, and it was determined that the liquid properties were almost the same.

[0079] (d) Fabrication of gas diffusion electrodes A long roll of gas diffusion electrode was manufactured using the gas diffusion electrode manufacturing apparatus shown in Figure 2. That is, the substrate (101) prepared in (a) above was unwound from an unwinder (102), and the coating liquid prepared in (b) above was applied to the entire length of the substrate using a coating machine (die coater, 104). At this time, the coating liquid was stirred in the container 1 and sent to the coating machine from the outlet below the tank using a pump. The pump flow rate was set so that the basis weight of the microporous layer after sintering was 15 g / m 2 The temperature of the coating liquid was maintained at 23±1°C. The substrate coated with the coating liquid then passed through a dryer (107) and a sintering machine (108) and was wound up as a gas diffusion electrode by a winding machine (109). The application of the coating liquid began after the coating liquid in the container 1 had been sufficiently degassed, and continued until air was drawn in from the bottom of the container during the transfer of the coating liquid, causing coating gaps and the generation of a large amount of bubbles in the coating film.

[0080] To measure the physical properties of the manufactured gas diffusion electrode, the wound gas diffusion electrode was unwound and samples were cut out every 200 m to measure the coating thickness, microporous layer weight, and in-plane gas diffusivity. Surface quality (number of through-holes, bubble point diameter) and power generation performance were measured by sampling from the starting point of the coating, that is, the area close to the core of the wound gas diffusion electrode.

[0081] (e) Measurement of coating thickness The difference between the thickness of the substrate prepared in (a) above and the thickness of the gas diffusion electrode manufactured in (d) above was defined as the coating thickness. For the measurement, a contact-type thickness meter (Mitutoyo Digimicro) was used, and the contact pressure was set to 0.15 MPa.

[0082] (f) Calculation of coating fluid usage efficiency After the gas diffusion electrode was produced as described in (d) above, the difference between the remaining amount of coating liquid after the production and the initial amount of coating liquid was subtracted to obtain the initial amount of coating liquid. The value (%) obtained by dividing this by the initial amount of coating liquid was used as the coating liquid usage efficiency.

[0083] (g) Measurement of the basis weight of the microporous layer The difference in basis weight between the gas diffusion electrode manufactured in (d) above and a 5 cm × 5 cm test piece of the substrate before the coating liquid was applied was measured, and the basis weight of the microporous layer (g / m 2 ) was decided.

[0084] (h) In-plane gas diffusion A Seika Corporation water vapor permeation diffusion tester (MVDP-200C) was used as an in-plane gas diffusion tester. In the piping system shown in Figure 6, first, only valve A (303) was opened, while valve B (305) was closed. Nitrogen gas 313 was flowed into primary piping A (302). A predetermined amount of gas (190 cc / min) was flowed into the mass flow controller (301), and the pressure controller (304) was adjusted to maintain a gas pressure of 5 kPa above atmospheric pressure. The gas diffusion electrode sample (308) fabricated in (d) above was placed on the sealant (312) between gas chamber A (307) and gas chamber B (309). Next, valve A (303) was closed, and valve B (305) was opened to allow nitrogen gas to flow into piping B (306). Nitrogen gas flowing into gas chamber A (307) moves through the gaps in the gas diffusion electrode sample (308) to gas chamber B (309), passes through pipe C (310), and is then released into the atmosphere through gas flow meter (311). The flow rate (cc / min) of the nitrogen gas flowing through the gas flow meter (311) at this time was measured, and this value was taken as the in-plane gas permeability.

[0085] (i) Measurement of the number of through holes The microporous layer surface of the gas diffusion electrode sample was observed using a stereomicroscope (Leica MC206) in epi-illumination mode with a 1x objective lens and a 2x intermediate lens, illuminating the sample from below. The number of through-holes (light passing through) was counted in a rectangular field of view of 6.8 mm x 4.5 mm on an image processing device. This was done for 330 fields of view, and the number of through-holes was counted at 100 cm 2 The number of through holes per unit area was calculated.

[0086] (j) Bubble point diameter Using a Perm Porometer manufactured by Porous Materials, a gas diffusion electrode sample punched to a diameter of 25 mm is immersed in a low-surface tension liquid (Galwick (USA)). The sample is then clamped in a special holder with a 1 / 2-inch diameter hole and set inside the cylinder of the clamping device. As the air pressure above the sample is increased, the low-surface tension liquid filling the through-holes of the sample is expelled sequentially downward, starting with the larger diameter pores. The diameter of the pore corresponding to the pressure at which the liquid is first expelled (bubble point pressure) is defined as the bubble point diameter. The relationship between bubble point pressure (kPa) and bubble point diameter (μm) is given by the following equation: Bubble point diameter (μm) = 45.6 ÷ bubble point pressure (kPa) This method complies with JIS K3832 and ASTM F316-86. Sixteen circular samples with a diameter of 25 mm were punched out from a 10 cm x 10 cm gas diffusion electrode, and the bubble point pressure (diameter) was measured. The minimum bubble point pressure and the maximum bubble point diameter were taken as the values ​​for that gas diffusion electrode. Incidentally, if pure water is used instead of the low surface tension liquid ("Galwick (USA)"), the so-called "water permeation pressure" is measured, but with the gas diffusion electrode of the present invention, the pressure became too high (over 150 kPa) and was not measurable.

[0087] (k) Porosity The porosity of the conductive porous substrate can be expressed as the average value of the porosity measured by randomly selecting 20 different locations in the microporous layer of the cross section perpendicular to the surface of the gas diffusion electrode using a microscope such as a scanning electron microscope, photographing the images at a magnification of approximately 20,000 times, and binarizing the void and non-void areas in each image. The cross section of the conductive porous substrate can be prepared using an ion milling device IM4000 manufactured by Hitachi High-Technologies Corporation or an equivalent device.

[0088] (l) Power generation performance The resulting gas diffusion electrodes were sandwiched between an electrolyte membrane and catalyst layer integrated product (a Gore Japan electrolyte membrane "Gore Select (registered trademark)" with Gore Japan catalyst layers "PRIMEA (registered trademark)" formed on both sides) so that the catalyst layer and the microporous layer were in contact with each other, and hot-pressed at 130°C to produce a membrane electrode assembly (MEA). This membrane electrode assembly was incorporated into a single fuel cell, and electricity was generated using a high-boiling-point solvent as a refrigerant at a cell temperature of 120°C, a gas pressure of 3 atmospheres, and humidification at a relative humidity of 90%, achieving a current density of 1.5 A / cm. 2 The voltage value at this time was used as an index of resistance to dry-up.

[0089] Example 1 A gas diffusion electrode was fabricated using the method described in (d) above. A vessel equipped with a double helical ribbon impeller (see Figure 1) was used as vessel 1. The impeller had a diameter of 0.90 m, a stirring speed of 16 rpm, and a peripheral speed of 0.75 m / s. Polypropylene (PP) beads were added to the coating solution during stirring, and visual observation of their movement revealed that the beads, which had sunk to the bottom of the vessel, reappeared on the surface, confirming the presence of vertical convection. The agitator was operated continuously until the coating solution in the tank could no longer be delivered to the applicator, and bubbles began to form on the coating surface. From the start of coating to the end of coating, the length of the carbon paper coated with the coating solution (coating yield) was 3,400 m. The coating solution utilization efficiency calculated using the method described in (f) above was 96%.

[0090] The microporous layer basis weight, coating thickness, and average value, standard deviation, and relative standard deviation of the in-plane gas permeability of the gas diffusion electrode, which were measured every 200 m from the start to the end of coating using the methods described in (e), (g), and (h) above, are shown in Table 1.

[0091] Furthermore, the number of through-holes, bubble point diameter, and power generation performance at high temperature (120°C) were measured for gas diffusion electrode samples taken from the area near the start of coating on the wound gas diffusion electrode roll, using the methods described in (i), (j), and (l) above. These values ​​are also shown in Table 1.

[0092] Example 2 A gas diffusion electrode was manufactured in the same manner as in Example 1, except that the rotation speed of the stirring blade was set to 5 rpm and the peripheral speed of the stirring blade's outer periphery was set to 0.24 m / s. During stirring, the presence of vertical convection was confirmed, as in Example 1. Almost the same coating liquid usage efficiency and longitudinal uniformity of each physical property as in Example 1 were obtained. The number of through-holes, bubble point diameter, and power generation performance were also similar to those in Example 1.

[0093] Example 3 A gas diffusion electrode was manufactured in the same manner as in Example 1, except that the rotation speed of the stirring blade was set to 2 rpm and the peripheral speed of the stirring blade's outer periphery was set to 0.09 m / s. During stirring, the presence of vertical convection was confirmed as in Example 1, and almost the same coating liquid usage efficiency and longitudinal uniformity of each physical property as in Example 1 were obtained. The number of through-holes, bubble point diameter, and power generation performance were also similar to those in Example 1.

[0094] (Comparative Example 1) A gas diffusion electrode was produced in the same manner as in Example 1, except that the rotation speed of the stirring blade was set to 19 rpm and the peripheral speed of the stirring blade was set to 0.89 m / s. During stirring, the presence of vertical convection was confirmed, as in Example 1.

[0095] (Comparative Example 2) After degassing the coating liquid, the operation of the stirrer was stopped, and the process from feeding the coating liquid to coating was carried out in the same manner as in Example 1, except that a gas diffusion electrode was produced.

[0096] (Comparative Example 3) A gas diffusion electrode was manufactured in the same manner as in Example 2, except that the shape of the stirring blade was changed to the anchor blade shown in Figure 4. In this example, polypropylene (PP) beads were added to the coating solution during stirring, and their movement was visually observed. Once the beads sank, they could not be seen again on the liquid surface, and it was determined that there was no vertical convection. In addition, some foaming was observed in the coating solution inside the container.

[0097] In Comparative Examples 1 to 3, the coating liquid usage efficiency was lower and the variations (relative standard deviation) in each physical property value were larger than in Examples 1 to 3. Furthermore, the number of through-holes on the microporous layer surface was larger in the Comparative Examples than in the Examples, and power generation performance at high temperatures also deteriorated.

[0098] [Table 1] [Industrial Applicability]

[0099] The manufacturing method of the present invention is effective in manufacturing a long gas diffusion electrode, can improve the use efficiency of the microporous layer coating liquid, and can produce gas diffusion electrodes with uniform physical properties related to the microporous layer, thereby reducing manufacturing costs and achieving uniform quality. [Explanation of symbols]

[0100] 1 container 2 Stirrer 21 Stirring blade 22 Stirring shaft 3 Pressure reducing means connection port 4 Coating liquid 5. Diameter of stirring blade 6 Tank inner diameter 7 Outlet 101 Conductive porous substrate 102 Unwinder 103 Guide roll (non-driven) 104 Coating machine 106 Back Roll (Drive) 107 Dryer 108 Sintering furnace 109 Winding machine 110 Insert 111 Insertion paper unwinder 113 Liquid transfer pump 114 filters 202 Microporous layer 203 Penetration of a microporous layer into a conductive porous substrate 204 Microporous layer thickness 205 Thickness of conductive porous substrate 301 Mass Flow Controller 302 Primary side piping A 303 Valve A 304 Pressure Controller 305 Valve B 306 Piping B 307 Gas Chamber A 308 Gas diffusion electrode sample 309 Gas Chamber B 310 Piping C 311 Gas flow meter 312 Sealing material 313 Nitrogen gas

Claims

1. A method for producing a gas diffusion electrode, comprising: a coating step of applying a microporous layer coating liquid containing conductive particles, a water-repellent resin, and a dispersion medium to a conductive porous substrate to form a microporous layer; a drying step of removing the dispersion medium from the microporous layer; and a sintering step of sintering the microporous layer and the water-repellent resin of the conductive porous substrate, In the coating step, a microporous layer coating liquid stirring device having a container for stirring and an agitator comprising at least a stirring shaft and a stirring blade; a coater for applying the microporous layer coating liquid to the conductive porous substrate; A method for producing a gas diffusion electrode, comprising: using an agitator for a gas diffusion electrode having piping and a liquid delivery device for delivering the microporous layer coating liquid from a microporous layer coating liquid agitator to a coater; delivering the microporous layer coating liquid by the liquid delivery device and applying the coating liquid while stirring the microporous layer coating liquid with the agitator under conditions that generate vertical convection in the microporous layer coating liquid in a container; and wherein the peripheral speed of the outermost periphery of the agitating blade during this process is 0.8 m / s or less.

2. 2. The method for producing a gas diffusion electrode according to claim 1, wherein the microporous layer coating liquid is a water-based coating liquid.

3. 3. The method for producing a gas diffusion electrode according to claim 1, wherein the viscosity of the microporous layer coating liquid is 1.0 Pa·s or more.

4. 4. The method for producing a gas diffusion electrode according to claim 1, wherein the microporous layer coating liquid has a shear thinning index (the ratio (a / b) of the viscosity value (a) at a shear rate of 17 ( / sec) to the viscosity value (b) at a shear rate of 127 ( / sec)) of 1.5 or more.

5. 5. The method for producing a gas diffusion electrode according to claim 1, wherein the shape of the stirring blade is a helical ribbon blade or a paddle blade.

6. 6. The method for producing a gas diffusion electrode according to claim 1, wherein the rotation speed of the stirring blade is 20 rpm or less.

7. A gas diffusion electrode comprising a conductive porous substrate and a microporous layer for a gas diffusion layer containing conductive particles and a water-repellent resin, wherein the conductive particles contained in the microporous layer are carbon black, and through-holes penetrating from the surface of the microporous layer through the gas diffusion electrode are 10 cm square (100 cm ２ 1. A gas diffusion electrode characterized in that the number of bubbles per electrode is less than 5 and the maximum bubble point diameter is 2.0 μm or less.

8. The through-holes that penetrate from the surface of the microporous layer to the gas diffusion electrode are 10 cm square (100 cm ２ 8. The gas diffusion electrode according to claim 7, wherein the number of bubble points is less than two per one electrode and the maximum bubble point diameter is 1.0 μm or less.

9. 9. The gas diffusion electrode according to claim 7, wherein the carbon black is acetylene black.

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