JP6750192B2 - Gas diffusion layer for polymer electrolyte fuel cells - Google Patents

Description

The present invention relates to a gas diffusion layer used in a polymer electrolyte fuel cell and a method for manufacturing the gas diffusion layer.

A polymer electrolyte fuel cell is a device that obtains an electromotive force by electrochemically reacting a fuel gas such as hydrogen and an oxidizing gas such as oxygen. The polymer electrolyte fuel cell includes hydrogen ions (protons). ) Has a polymer electrolyte membrane which selectively conducts. Further, two sets of gas diffusion electrodes having a catalyst layer containing a carbon powder carrying a noble metal catalyst as a main component and a gas diffusion electrode base material are joined from both sides to the both sides of the polymer electrolyte membrane.

A joined body composed of such a polymer electrolyte membrane and two sets of gas diffusion electrodes is called a membrane-electrode assembly (MEA: Membrane Electrode Assembly). Further, on both outer sides of the MEA, separators having gas flow paths for supplying the fuel gas or the oxidizing gas and discharging the generated gas and the excess gas are installed.

The gas diffusion electrode substrate is mainly required to have the following three functions. The first function is to uniformly supply the fuel gas or the oxidizing gas to the noble metal-based catalyst in the catalyst layer from the gas flow path formed in the separator arranged on the outside thereof. The second function is to discharge the water generated by the reaction in the catalyst layer. The third function is a function of conducting electrons necessary for the reaction in the catalyst layer or electrons generated by the reaction in the catalyst layer to the separator. As a base material satisfying these functions, a base material made of a carbonaceous material and having a porous structure is usually used. Specifically, a base material using carbon fibers such as carbon paper, carbon fiber cloth, and carbon fiber felt is generally used. These base materials are not only highly conductive due to carbon fibers, but also porous materials, and therefore have high permeability to liquids such as fuel gas and generated water, and are therefore suitable materials for the gas diffusion layer.

For the purpose of reducing the contact resistance between the electrode catalyst layer and the porous carbon electrode base material such as the carbon paper and the carbon cloth mentioned above, and efficiently discharging the generated water generated during power generation, carbon fine particles and a water repellent agent. In some cases, a coating layer composed of is provided between the porous carbon electrode substrate and the electrode catalyst layer. Patent Document 1 discloses a gas diffusion layer provided with a water repellent layer as the coating layer.

JP, 2010-129451, A

However, since the gas diffusion layer formed by this method has a remarkably high density of the coating layer as compared with the gas diffusion layer base material, unintentional cracks are generated in the coating layer when wound into a roll. Therefore, it was difficult to manufacture continuously. The present invention provides a gas diffusion layer that can be wound into a roll, overcoming the above-mentioned problems and intentionally providing fine cracks in the coating layer so that the structure of the coating layer does not change before and after winding. The purpose is to

Specifically, the above problems are solved by the following inventions (1) to (8).

(1) On at least one surface of a porous carbon electrode substrate, carbon powder and a water repellent agent are formed, and 25 to 1000 cracks having a length of 0.001 to 1 mm and a width of 0.05 to 10 μm are formed on the surface. Gas diffusion layer provided with a coating layer having a /m ² .

(2) The gas diffusion according to (1) above, wherein the thickness of the porous electrode base material forming the gas diffusion layer is 50 to 250 μm, and the thickness of the coating layer formed on at least one surface is 5 to 100 μm. layer.

(3) A roll-shaped product of the gas diffusion layer, wherein the gas diffusion layer according to (1) or (2) is wound around a core material having an outer diameter of 84.2 to 167.4 mm in a roll shape.

(4) The roll-shaped material of the gas diffusion layer according to (3) above, wherein the gas diffusion layer is wound so that the coating layer is arranged outside the porous carbon electrode substrate with respect to the core material.

(5) The roll-shaped product of the gas diffusion layer according to (3) above, in which the gas diffusion layer is wound so that the coating layer is arranged inside the porous carbon electrode substrate with respect to the core material.

(6) The roll-shaped material of the gas diffusion layer according to any one of (3) to (5), wherein the core material is paper.

(7) The roll-shaped material of the gas diffusion layer according to any one of (3) to (5), wherein the core material is a resin.

(8) The roll-shaped product of the gas diffusion layer according to any one of (3) to (7) above, wherein a protective layer having a thickness of 5 to 100 μm is wound around the core material together with the gas diffusion layer.

(9) A method for producing a gas diffusion layer, which comprises the following steps [1] to [4].

Step [1]: A step of obtaining a coating liquid by mixing and stirring a liquid consisting of carbon powder, a water repellent, a surfactant, and water with a stirrer.

Step [2]: A step of applying the coating liquid obtained in the above step [1] onto the porous carbon electrode substrate to form a uniform coating film on the porous carbon electrode substrate.

Step [3]: The porous carbon electrode base material on which the coating film is formed is dried in an environment of 150°C to 300°C to remove water in the coating film to form a coating layer on the porous carbon electrode base material. The process of doing.

Step [4]: A step of heating the porous carbon electrode substrate having the coating layer at 200 to 400° C. to obtain a gas diffusion layer.

To provide a gas diffusion layer that can be wound into a roll, which is a simple manufacturing method, but does not change the structure of the coating layer before and after winding by intentionally providing fine cracks in the coating layer. You can

It is a scanning electron microscope photograph of the gas diffusion layer of the present invention.

Hereinafter, the present invention will be described in detail.

1. Method of Manufacturing Porous Carbon Electrode The porous carbon electrode of the present invention can be manufactured by a manufacturing method including the following steps [1] to [4].

Step [1]: A step of obtaining a coating liquid by mixing and stirring a liquid consisting of carbon powder, a water repellent, a surfactant, and water with a stirrer.

Step [2]: A step of applying the coating liquid obtained in the above step [1] onto the porous carbon electrode substrate to form a uniform coating film on the porous carbon electrode substrate.

Step [3]: The porous carbon electrode base material on which the coating film is formed is dried in an environment of 150°C to 300°C to remove water in the coating film to form a coating layer on the porous carbon electrode base material. The process of doing.

Step [4]: A step of heating the porous carbon electrode substrate having the coating layer at 200 to 400° C. to obtain a gas diffusion layer.

<Step [1]: A step of obtaining a coating liquid by mixing and stirring a liquid consisting of carbon powder, a water repellent, a surfactant, and water with a stirrer>
As the carbon powder to be used, for example, graphite powder or carbon black can be used. For example, as carbon black, acetylene black (for example, Denka black manufactured by Denki Kagaku Kogyo Co., Ltd.), Ketjen black (for example, Ketjen Black EC manufactured by Lion Co., Ltd.), furnace black (for example, Vulcan XC72 manufactured by CABOT), etc. are used. Can be used. It is preferable to use carbon black from the viewpoint of exhibiting higher conductivity.

Examples of the water repellent include fluororesin. Examples of the fluororesin include tetrafluoroethylene-hexafluoropropylene copolymer, polytetrafluoroethylene (PTFE), tetrafluoroethylene-ethylene copolymer, and the like, and polytetrafluoroethylene (PTFE) is particularly preferable. PTFE may be dispersed in water with a surfactant, or a dispersion previously dispersed may be used.

Known surfactants can be used. Examples thereof include nonionic surfactants such as polyoxyethylene (10) octyl phenyl ether (for example, Triton X-100 manufactured by ACROS ORGANICS), alkyl ethers and alkyl phenyl ethers. From the viewpoint of handleability and decomposition temperature, it is preferable to use polyoxyethylene (10) octyl phenyl ether.

A known method can be used as a method for preparing a coating liquid from carbon powder, a water repellent, a surfactant, and water. It is obtained by respectively preparing and mixing a dispersion liquid of carbon powder and a dispersion liquid of a water repellent. In order to obtain the carbon dispersion liquid, water is mixed with the carbon powder. At this time, it is preferable to add an organic solvent or a surfactant in order to improve the wettability of the carbon powder and improve the dispersibility. As such an organic solvent, lower alcohols and acetone are preferred. The amount of the surfactant added may be 0.1 wt% or more with respect to the entire coating liquid in order to improve the dispersibility of the carbon powder, and if the addition amount is too large, foaming will occur, so that 5 wt% The following is preferable. A thickener and the like can be added depending on the desired viscosity. As a device used for stirring, a general stirrer, for example, a disper, a homogenizer, a sand mill, a jet mill, a ball mill, a bead mill, or the like can be used. It is preferable to use a disperser, a homogenizer or the like from the viewpoint of easy operation and shortening of the processing time. To make the water repellent into fibers, keep the stirring temperature of the coating liquid in which the carbon powder and the water repellent are dispersed at 30° C. or higher, and at a stirring speed of 5000 rpm or higher when using a disper, for 15 minutes or longer. Mixing and stirring are preferable.

<Step [2]: Step of applying the coating liquid obtained in the above step [1] on the porous carbon electrode substrate to form a uniform coating film on the porous carbon electrode substrate>

<Treatment of porous carbon electrode substrate>
For the water repellent treatment for imparting water repellency to the porous carbon electrode substrate, a dispersion liquid in which particles of a water repellent agent such as a fluororesin are dispersed in a solvent is used. When water is used as the solvent, the water-repellent agent is not dispersed in water as it is, and therefore it is dispersed in water with an appropriate surfactant. Further, as the dispersion liquid, a dispersion or the like in which a water repellent is previously dispersed can be used.

<<Formation of coating film>>
As a coating method for forming a coating film on the porous carbon electrode substrate, a conventionally known method can be used, for example, a bar coating method, a blade method, a screen printing method, a spray method, Curtain coating method and roll coating method can be used. The thickness of the coating film capable of forming a uniform coating film on the porous carbon electrode substrate by these methods is preferably 50 to 2000 μm. If the thickness of the coating film is less than 50 μm, it becomes difficult to obtain a film having a uniform thickness, and if it is more than 2000 μm, unintended large cracks are likely to occur in the coating layer after drying, which is not preferable. A more preferable thickness range of the coating film is 50 to 1000 μm.

<Step [3]: The porous carbon electrode substrate having a coating film formed thereon is dried in an environment of 150° C. to 300° C. to remove water in the coating film to form a coating layer on the porous carbon electrode substrate. Forming process>
In the present invention, the porous carbon electrode substrate on which the coating film is formed is placed in an environment of 150°C to 300°C to dry the coating film. For example, a plate heater, a heating roll, a hot air dryer, an IR heater, or the like can be used to create an environment of 150°C to 300°C.

In the present invention, the atmospheric temperature at the time of drying is preferably in the range of 150°C to 300°C, more preferably 200 to 300°C, in order to intentionally generate cracks in the coating film. If the drying temperature is lower than 150°C, rapid evaporation of the solvent does not occur and cracks cannot be generated. Also, if the drying temperature is higher than 300°C, the evaporation rate of the solvent is too fast, resulting in large cracks. Will occur in the coating film, and the strength of the coating film will decrease. In consideration of productivity, the drying time is preferably 0.5 minutes to 20 minutes, more preferably 0.5 minutes to 10 minutes.

<Step [4]: Step of heating the porous carbon electrode substrate having the coating layer to 200 to 400° C. to obtain a gas diffusion layer>
In the present invention, the gas diffusion layer is produced by firing the dried “coated film-formed porous carbon electrode substrate” in an environment of 300 to 400° C.

In this baking step, first, the dispersant such as a surfactant contained in the porous carbon electrode substrate and the coating film is eliminated, and in addition, the water repellent is heated up to around the melting point to repel water. By melting the agent particles and controlling their shape, the pore structure control of the coating layer and the binding of the carbon powder are strengthened. Therefore, the temperature is preferably in the range of 300 to 400°C, more preferably 340 to 400°C. The firing time is preferably 5 to 90 minutes, more preferably 10 to 60 minutes.

<< Porous carbon electrode substrate >>
According to the production method of the present invention, it is possible to produce a porous carbon electrode for a polymer electrolyte fuel cell having low electric resistance and good drainage from a porous carbon electrode substrate. Any porous carbon electrode substrate can exhibit the above effects by using the technique of the present invention as compared with the conventional manufacturing technique.

As described above, any porous carbon electrode substrate in the present invention can be used.

As the porous carbon electrode base material, it is possible to use all conductive porous materials such as conductive paper, cloth, and non-woven fabric made of conductive powder such as carbon powder, carbon fiber, metal fiber and resin. Specifically, commercially available carbon paper or the like can be used, but a porous carbon electrode base material in which carbon fibers are bound by carbon can also be used. The carbon that binds the carbon fibers includes carbon fiber precursor fibers and resins, and there is a method of carbonizing them by treating them at high temperatures. A carbon fiber sheet can be prepared from carbon fibers, fibers serving as a carbon source, a resin, etc., and a porous carbon electrode substrate in which carbon fibers are bound by carbon can be manufactured through a molding/carbonization process. It is desirable that these steps are continuously manufactured in terms of quality and productivity. Further, not only the above-mentioned porous carbon electrode base material, but also a porous carbon electrode base material that does not have a carbonization step and has a low energy cost can be used. Examples of these are porous carbon electrode base material obtained by binding a carbon fiber web or carbon or other fine conductive material bound by a binder such as resin to a carbon fiber web bound by a binder filled with conductive material particles. and so on.

<Method for producing porous carbon electrode substrate>
In the production of the sheet-like material, a papermaking method such as a wet method in which the carbon fiber (A) is dispersed in a liquid medium for papermaking, or a dry method in which the carbon fiber (A) is dispersed in the air and accumulated. The method can be applied. The wet method is preferred.

By dispersing the carbon fiber precursor fiber (b) and/or the fibrillar fiber (b′) together with the carbon fiber (A), the carbon fiber (A) and the carbon fiber precursor fiber (b) and/or the fibrillar state are dispersed. Entangling with the fibers (b′) improves the strength of the sheet-like material, and can be substantially binder-free.

In the present invention, a small amount of organic polymer compound may be used as a binder. The organic polymer compound used as the binder is not particularly limited, but examples thereof include polyvinyl alcohol (PVA), and a polyester or polyolefin binder that is heat-sealed. The binder may be solid such as fibers or particles or liquid. The content of the binder is preferably 100 g/m ² or less, more preferably 50 g/m ² or less, and particularly preferably 30 g/m ² or less. The method of adding the binder is not particularly limited.

Hereinafter, an example of a method for producing a porous carbon electrode substrate using carbon fiber will be described in detail. The porous carbon electrode substrate is manufactured through the following procedures (1) to (4).

Procedure (1): Process for producing a paper body in which carbon fibers (A) and carbon fiber precursor fibers (b) and/or fibrillar fibers (b') are dispersed <carbon fibers (A)>
The carbon fiber (A) can be used regardless of its raw material, but is selected from polyacrylonitrile (hereinafter abbreviated as PAN)-based carbon fiber, pitch-based carbon fiber, rayon-based carbon fiber, and phenol-based carbon fiber 1 It is preferable to contain three or more carbon fibers, and it is more preferable to contain PAN-based carbon fibers or pitch-based carbon fibers. The average diameter of the carbon fibers (A) is preferably about 3 to 30 μm, more preferably 4 to 20 μm, and further preferably 4 to 8 μm, from the viewpoint of surface smoothness and conductivity as a gas diffusion layer. The length of the carbon fiber (A) is preferably 2 to 12 mm, more preferably 3 to 9 mm, from the viewpoint of dispersibility during papermaking and mechanical strength of the gas diffusion layer.

<Carbon fiber precursor fiber (b)>
The carbon fiber precursor fiber (b) is a long fiber-like carbon fiber precursor fiber cut into an appropriate length. From the viewpoint of dispersibility, the fiber length of the carbon fiber precursor fiber (b) is preferably about 2 to 20 mm. The cross-sectional shape of the carbon fiber precursor fiber (b) is not particularly limited, but from the viewpoint of mechanical strength after carbonization and manufacturing cost, one having a high roundness is preferable. The diameter of the carbon fiber precursor fiber (b) is preferably 5 μm or less in order to prevent breakage due to shrinkage during carbonization.

As the polymer used as the carbon fiber precursor fiber (b), the residual mass in the carbonization treatment step is preferably 20% by mass or more. Examples of such polymers include acrylic polymers, cellulose polymers, and phenolic polymers.

Considering the spinnability and the ability to bond the carbon fibers (A) to each other from a low temperature to a high temperature, the large residual mass during carbonization, and further the fiber elasticity and the fiber strength during the entanglement treatment described later, acrylonitrile is considered. It is preferable to use an acrylic polymer containing a unit of 50% by mass or more. Therefore, as the carbon fiber precursor fiber (b), acrylic fiber and acrylic fiber (containing 50% by mass or more of acrylonitrile unit) are preferable.

As the carbon fiber precursor fiber (b), one kind may be used, or two or more kinds of carbon fiber precursor fiber (b) having different fiber diameters and polymer types may be used.

<Fibril-like fiber (b')>
As the fibrillar fiber (b′), any fiber can be used without distinction between natural fiber and synthetic fiber. For example, it includes fibrillar carbon precursor (b'-1) containing acrylic as a main component to wood pulp which is a natural fiber. Above all, since it is preferable that the metal content is small, the fibrillar fiber (b′) is preferably a synthetic fiber. More preferably, fibrillar carbon precursor fiber (b'-1) or the like can be used. These may be used alone or in combination. Further, in order to improve the carbonization yield, it is preferable to use the fibrillar carbon precursor fiber (b′-1) shown below.

The fibrillar carbon precursor fiber (b′-1) is a long fiber-like easily splittable sea-island composite fiber cut into an appropriate length, and is beaten by a refiner or pulper to be fibrillated. The fibrillar carbon precursor fiber (b′-1) is manufactured by using two or more kinds of different polymers that are soluble and incompatible in a common solvent, and at least one kind of the polymer is carbonized. The residual mass in the process is preferably 20% by mass or more.

Among the polymers used for the easily splittable sea-island composite fiber, those having a residual mass of 20% by mass or more in the carbonization treatment step include acrylic polymers, cellulose polymers and phenolic polymers. Above all, it is preferable to use an acrylic polymer containing 50% by mass or more of an acrylonitrile unit from the viewpoint of spinnability and residual mass in the carbonization treatment step.

The cross-sectional shape of the fibrillar fibers (b') is not particularly limited. The fineness of the fibrillar fibers (b′) is preferably 1 to 10 dtex in order to prevent dispersibility and breakage due to shrinkage during carbonization. The average fiber length of the fibrillar fibers (b′) is preferably 1 to 20 mm from the viewpoint of dispersibility.

<Manufacture of papermaking body>
The following method can be used in the production of the papermaking body. The carbon fiber (A) cut into a suitable length is uniformly dispersed in water, the dispersed carbon fiber is made into a paper, and the made carbon fiber sheet is dipped in an aqueous dispersion of polyvinyl alcohol and dipped. Pull up the dried sheet to dry. The polyvinyl alcohol serves as a binder that binds the carbon fibers together, and when the carbon fibers are dispersed, a carbon fiber sheet in which the carbon fibers are bound by the binder is manufactured. As the binder, styrene-butadiene rubber, epoxy resin or the like can be used as well.

As a method for producing a paper body in which carbon fibers (A) and carbon fiber precursor fibers (b) and/or fibrillar fibers (b′) are dispersed, carbon fibers (A) and carbon fibers in a liquid medium are used. Wet method of dispersing precursor fiber (b) and/or fibrillar fiber (b') for papermaking, carbon fiber (A) in air, carbon fiber precursor fiber (b) and/or fibrillar fiber A paper-making method such as a dry method in which (b′) is dispersed and accumulated is applicable. However, the wet method is preferably used from the viewpoint of high uniformity of the paper body.

The mixing ratio of the carbon fiber (A) and the carbon fiber precursor fiber (b) and/or the fibrillar fiber (b') is 100 parts by weight of the carbon fiber (A), and the carbon fiber precursor fiber (b). It is preferable that the total amount of the fibrillar fibers (b′) is 20 to 100 parts by weight. When the total amount of the carbon fiber precursor fibers (b) and the fibrillar fibers (b') is small, the strength of the papermaking body is low, and the total amount of the carbon fiber precursor fibers (b) and the fibrillar fibers (b') is large. Then, the electrical conductivity of the resulting porous carbon electrode substrate will be low. Further, the ratio of the carbon fiber precursor fiber (b) and the fibrillar fiber (b') is 25 to 100 parts by weight of the fibrillar fiber (b') with respect to 100 parts by weight of the carbon fiber precursor fiber (b). It is preferable to be included in the ratio of.

The carbon fiber precursor fiber (b) and/or the fibrillar fiber (b′) also help the carbon fibers (A) to open into single fibers and prevent the opened single fibers from re-converging. ) Is used. If necessary, a binder may be used for wet papermaking.

The binder has a role as a sizing agent that holds each component together in the precursor sheet containing the carbon fiber (A) and the carbon precursor fiber (b). As the binder, polyvinyl alcohol (PVA), polyvinyl acetate or the like can be used. In particular, polyvinyl alcohol is preferable because it has excellent binding force in the papermaking process and the carbon fiber (A) is less likely to fall off. In the present invention, the binder may be used in the form of fibers.

In the present invention, even if papermaking is performed without using a binder, it is possible to obtain an appropriate entanglement between the carbon fiber (A) and the carbon fiber precursor fiber (b) and/or the fibrillar fiber (b′).

As a liquid medium in which the carbon fibers (A) and the carbon fiber precursor fibers (b) and/or the fibrillar fibers (b′) are dispersed, for example, the carbon precursor fibers (b) such as water and alcohol are not dissolved. The medium may be mentioned. Among these, it is preferable to use water from the viewpoint of productivity.

It is preferable to use a medium such as water at a rate such that the fiber concentration in the slurry in which the fiber is dispersed is about 1 to 50 g/L. When the fiber concentration in the slurry is low, the papermaking speed must be slowed down, the productivity becomes poor, and when the fiber concentration is too high, the dispersibility of the fiber in the slurry decreases, A lump is easily generated, and a paper body having a large uneven weight is obtained.

Examples of the method for mixing the carbon fiber (A) and the carbon fiber precursor fiber (b) and/or the fibrillar fiber (b′) include a method of stirring and dispersing in water and a method of directly mixing them, but they are uniform. From the viewpoint of dispersion in water, a method of diffusion dispersion in water is preferable. By mixing the carbon fiber (A) with the carbon fiber precursor fiber (b) and/or the fibrillar fiber (b′) and making a paper to produce a papermaking body, it is possible to improve the strength of the papermaking body. it can. Further, it is possible to prevent the carbon fibers (A) from peeling off from the precursor sheet during the production thereof and changing the orientation of the carbon fibers (A).

Step (2) Step of performing entanglement treatment on the papermaking body The entanglement treatment is not always necessary, but by performing the entanglement treatment on the sheet-like material, the carbon fibers (A) and the carbon fiber precursor fibers (b) and/or fibrils are formed. A sheet (entangled structure sheet) having an entangled structure in which the fibers (b′) are entangled three-dimensionally can be formed.

The entanglement treatment can be selected as necessary from the method of forming the entangled structure and is not particularly limited. Mechanical entangling method such as needle punching method, high pressure liquid injection method such as water jet punching method, high pressure gas injection method such as steam jet punching method, or a combination thereof can be used. The breakage of the carbon fiber (A) and the breakage of the carbon fiber precursor fiber (b) and/or the fibrillar fiber (b′) in the entanglement treatment step can be easily suppressed, and an appropriate entanglement property can be obtained. The high-pressure liquid jet method is preferable because it can be easily obtained.

Since the tensile strength of the papermaking body is improved by the entanglement treatment step, it is not necessary to use a binder such as polyvinyl alcohol usually used in papermaking, and the tensile strength of the sheet can be maintained even in water or in a wet state.

Step (3): a step of impregnating a paper body with a resin, drying and molding <resin>
The resin with which the papermaking body is impregnated can be appropriately selected from known resins that can bind the carbon fibers of the gas diffusion layer at the carbonization stage. When producing a porous carbon electrode substrate having a carbonization step, phenol resin, epoxy resin, furan resin, pitch and the like are preferable from the viewpoint that they are likely to remain as a conductive substance after carbonization. Particularly preferred is a phenol resin having a high carbonization rate. When manufacturing a porous carbon electrode substrate having no carbonization step, any thermoplastic or thermosetting resin can be used. From the viewpoint of enhancing the water repellency of the porous carbon electrode substrate, fluororesin is preferable. Further, it is also effective to mix carbon powder with these resins for the purpose of further improving the conductivity of the porous carbon electrode base material regardless of the presence or absence of the carbonization step. Examples of the carbon powder include scaly graphite, scaly graphite, earthy graphite, artificial graphite, expanded graphite, expanded graphite, flake graphite, lump graphite, spherical graphite, and other graphite particles, and further carbon black, fullerene, carbon. Examples include nanotubes. Although not particularly limited, graphite particles and carbon black are more preferable among the above carbon powders. One or more of these may be used.

<Impregnation method>
As a method for impregnating the thermosetting resin, a known method can be used. For example, a dip method, a kiss coat method, a spray method, a curtain coat method or the like can be used. Particularly, from the viewpoint of manufacturing cost, it is preferable to use the spray method or the curtain coating method.

<Drying/molding process>
As a drying method, a known technique can be used. A drum drying method of contacting with a heated roll for drying or a drying method using hot air can be used. Drying by a non-contact method is preferable because of easy maintenance. As the drying temperature, a temperature range in which the resin does not cure is 60 to 110°C, more preferably 70 to 100°C.

The step of molding the paper body after resin impregnation and drying is important. When producing a porous carbon electrode substrate having a carbonization step, the carbon fiber (A) in the precursor sheet is thereby converted into the carbon fiber precursor fiber (b) and/or the fibrillar carbon precursor fiber (b′). By fusing at -1) and curing the thermosetting resin, a strong conductive path of the carbonized porous carbon electrode substrate is formed. When manufacturing a porous carbon electrode substrate without a carbonization step, the product size is determined by the molding step, so the molten state of the fibrillar carbon precursor fiber (b'-1) and the resin is controlled. There must be. The manufacturing process of the carbonization step is completed by performing heat treatment in an atmosphere of 200 to 400° C. after molding.

As the molding method, any technology can be applied as long as it is a technology capable of uniformly heating and pressing the papermaking body. For example, a method in which smooth rigid plates are applied to both sides of a papermaking body to perform hot pressing, a method using a continuous roll pressing device, or a continuous belt pressing device can be mentioned.

The heating temperature in the heat and pressure molding is preferably less than 200°C, and more preferably 120 to 190°C in order to effectively smooth the surface of the precursor sheet.

The molding pressure is not particularly limited, but when the content ratio of the carbon fiber precursor fiber (b) and/or the fibrillar fiber (b′) in the papermaking body is high, the surface of the sheet Y can be easily formed even if the molding pressure is low. Can be smoothed. At this time, if the pressing pressure is increased more than necessary, there is a possibility that the carbon fiber (A) is destroyed during the heat and pressure forming, the structure of the porous carbon electrode substrate becomes too dense, and the like. is there. The molding pressure is preferably about 20 kPa to 10 MPa.

The time for heat and pressure molding can be set to, for example, 30 seconds to 10 minutes. When sandwiching the papermaking body between two rigid plates or when heat-pressing with a continuous roll pressing device or a continuous belt pressing device, carbon fiber precursor fibers (b) and/or fibrils are formed on the rigid plates or rolls or belts. It is preferable to apply a release agent in advance so that the carbon precursor fibers (b′) and the like do not adhere, and to sandwich a release paper between the papermaking body and the rigid plate or roll or belt.

Step (4): A step of carbonizing the precursor sheet obtained in the above step (3) at 2000 to 3000° C. in a nitrogen atmosphere to produce a porous carbonaceous electrode substrate .

<Carbonization>
The carbonization treatment carbonizes the carbon fiber precursor fiber (b) and/or the fibrillar carbon precursor fiber (b′) and the thermosetting resin in the precursor sheet. The carbonization treatment is preferably performed in an inert gas in order to enhance the conductivity of the porous carbon electrode substrate. The carbonization treatment is usually performed at a temperature of 1000°C or higher. The carbonization treatment temperature range is preferably 1000 to 3000°C, more preferably 1000 to 2200°C. The carbonization treatment time is, for example, about 10 minutes to 1 hour. Further, before the carbonization treatment, a pretreatment by firing in an inert atmosphere of about 300 to 800° C. can be performed.

In the case of carbonizing the precursor sheet that is continuously manufactured, it is preferable to continuously perform carbonization over the entire length of the precursor sheet from the viewpoint of reducing the manufacturing cost. If the porous carbon electrode substrate is long, the handling property is high, the productivity of the porous carbon electrode substrate is high, and the subsequent production of the membrane-electrode assembly (MEA) can be continuously performed. Therefore, the manufacturing cost of the fuel cell can be reduced. Further, it is preferable to continuously wind up the manufactured porous carbon electrode base material from the viewpoint of productivity of the porous carbon electrode base material and the fuel cell and reduction of manufacturing cost.

A porous carbon electrode base material can be obtained through the procedure described above. The procedure (2) and the procedure (3) can be omitted.

<Method of manufacturing porous carbon electrode substrate without carbonization step>
By omitting the carbonization step, the energy cost can be significantly reduced as compared with the case where carbonization is performed. In order to suppress the decrease in conductivity due to the omission of the carbonization step, it is necessary to introduce a further conductive substance. As described above, a method of adding and fixing the conductive substance or the like to the paper body in which the carbon fibers are dispersed, or preparing a slurry composed of the conductive substance and a binder resin, and after forming them into a film, heat treatment is performed to obtain porous carbon. There is a method of manufacturing an electrode base material. In the case of the former method, according to the method for producing a porous carbon electrode substrate having the above-mentioned carbonization step, a conductive material is added in the manner of resin impregnation of the papermaking body, and then press molding is performed. The porous carbon electrode base material can be manufactured by fixing with. Further, also in the latter production method, in the same manner as in the slurry preparation method for manufacturing the papermaking body, a single or a plurality of conductive materials are selected, and a slurry is prepared by mixing with a binder material in a solution, A porous carbon electrode substrate can be manufactured by performing drying and heat treatment after forming a film using a known coating technique. In addition, the conductive material provided for these is not particularly limited, and for example, in the case of carbon fiber, polyacrylonitrile-based (PAN-based) carbon fiber, pitch-based carbon fiber, rayon-based carbon fiber, other, carbon black, Carbon nanotubes or the like can be used as appropriate. The type to be used is not limited and may be used alone or may be selected in plural. A resin can be used as the binder for fixing the conductive substance. As the resin, a water-repellent fluorine-based or silicone-based resin is suitable. In preparing the above-mentioned slurry, water, acetone, ethanol, methanol or the like can be appropriately used as the solvent of the slurry, but from the viewpoint of reducing environmental load and cost of the manufacturing apparatus, use water as the solvent. Is most preferred. Further, in order to improve the dispersibility of the conductive substance and the binder substance in the slurry, additives such as a surfactant and a sticky agent may be appropriately used.

2. Gas diffusion layer The porous carbon electrode obtained by the production method of the present invention has a water repellent agent in which carbon powder and fiber are formed on at least one surface of a porous carbon electrode substrate in which carbon fibers are bound by carbon. Is a gas diffusion layer having a coating layer formed of.

<A gas diffusion layer in which a coating layer made of carbon powder and a fibrous water repellent is formed on at least one surface of a porous carbon electrode substrate>
In the present invention, "a porous carbon electrode substrate having a coating layer formed of carbon powder and a water repellent on at least one surface thereof" is referred to as a "gas diffusion layer". The coating layer may be formed on one surface or both surfaces of the porous electrode substrate. When forming a coating layer only on one surface of the porous carbon electrode substrate, from the viewpoint of reducing the contact resistance between the catalyst layer and the porous carbon electrode substrate, with the catalyst layer in the polymer electrolyte fuel cell It is preferable to provide a coating layer on the surface of the porous electrode base material on the contact side.

As the carbon powder used for the coating layer, for example, graphite powder or carbon black can be used. For example, acetylene black (for example, Denka black manufactured by Denki Kagaku Kogyo Co., Ltd.), Ketjen black (for example, Ketjen Black EC manufactured by Lion Co., Ltd.), furnace black (for example, Vulcan XC72 manufactured by CABOT) can be used. .. The carbon powder is preferably used so that the concentration when the carbon powder is dispersed in the solvent is 5 to 30%. Examples of the water repellent include fluororesins and silicone resins, which can be used by dispersing them in a solvent such as water. A fluororesin is particularly preferable because of its high water repellency. Examples of the fluororesin include tetrafluoroethylene-hexafluoropropylene copolymer, polytetrafluoroethylene (PTFE), and tetrafluoroethylene-ethylene copolymer, and PTFE is particularly preferable. Regarding the proportion of the water repellent, it is preferable to use the water repellent such that the concentration of the water repellent when dispersed in the solvent is 5 to 60%. In the present invention, since the water repellent agent is made into fibers, PTFE produced by emulsion polymerization is preferable, and among them, the dispersion type is preferably used.

Water or an organic solvent can be used as a solvent for dispersing the carbon powder and the water repellent. From the viewpoint of the danger of organic solvent, cost and environmental load, it is preferable to use water. When using an organic solvent, it is preferable to use a lower alcohol, acetone, or the like, which is a solvent miscible with water. The ratio of these organic solvents used is preferably 0.5 to 2 with respect to 1 part of water.

The coating layer composed of carbon powder and a water repellent is carbon powder bonded by a water repellent which is a binder. In other words, carbon powder is incorporated into the network formed by the water repellent, and has a fine network structure. Since a part of the composition permeates into the porous carbon electrode substrate when forming the coating layer, it is difficult to define a clear boundary line between the coating layer and the porous carbon electrode substrate. In (1), a portion of the coating layer composition where the porous carbon electrode substrate is not soaked, that is, only a layer composed of carbon powder and a water repellent is defined as a coating layer. Since the coating layer of the present invention contains a fibrous water repellent agent, the network structure becomes stronger and not only the strength of the coating layer is improved, but also the fibrous water repellent agent and the porous carbon electrode. The entanglement with the base material improves the adhesion between the coating layer and the porous carbon electrode base material, and a gas diffusion layer for a polymer electrolyte fuel cell having a high peel strength of the coating layer can be obtained. The gas diffusion layer of the present invention has a coating layer composed of carbon powder and a water repellent agent on one of the surfaces of the porous carbon electrode substrate. Although it may have the coating layer on both sides, single-side coating is preferable because productivity may decrease due to an increase in the number of processes and gas diffusion and drainage may decrease due to having coating layers on both sides. .. The surface on which the coating layer is formed may be either surface, but it is preferably a surface having a certain degree of surface roughness in order to form a strong coating layer. However, this is not limited to the case where a gas flow path is formed on one surface of the porous carbon electrode substrate, and it is preferable to form it on the other smooth surface.

<25-1000 cracks/meter on the surface of at least one surface of the porous carbon electrode substrate, which are made of carbon powder and a water repellent and have a length of 0.001 to 1 mm and a width of 0.05 to 10 μm. ² gas diffusion layer provided with a coating layer>
The term "crack" as used herein refers to a crack in the coating layer. The degree of occurrence of these cracks can be changed by changing the removal rate of the solvent removed from the coating film when the coating layer is dried. The crack length is preferably 0.001 to 1 mm, and more preferably 0.001 to 0.05 mm. If the crack is smaller than 0.001 mm, the flexibility of the coating layer due to the crack does not appear, and if it is larger than 1 mm, the drainage property of the coating layer is significantly deteriorated. The width of the crack is preferably in the range of 0.05 to 10 μm. If it is less than 0.05 μm, the flexibility of the coating layer due to cracks does not appear, and if it is more than 10 μm, the pore diameter is the same as the pore diameter size of the porous carbon electrode substrate, so the water retention effect of the coating layer decreases. Will end up. A more preferable crack width is 0.05 to 5 μm. The number of cracks is preferably 25 to 1000/m ² . When it is less than 25/m ² , the flexibility of the coating layer is insufficient, and the structural change of the coating layer becomes significant before and after winding in the winding test described later. If the number is 1000 or more, the strength of the coating layer is significantly reduced. The more preferable number of cracks is 25 to 500/m 2.

<Thickness of gas diffusion layer>
The thickness of the gas diffusion layer is preferably in the range of 55 to 350 μm in order to exhibit good electric conductivity and drainage property. If it is 55 μm or more, handling is possible, and if it is 350 μm or less, good electric conductivity is obtained. A more preferable thickness is in the range of 100 to 250 μm. The thickness of the porous electrode substrate forming the gas diffusion layer is preferably 50 to 250 μm, and the thickness of the coating layer formed on at least one surface is preferably 5 to 100 μm. If the thickness of the porous electrode base material is smaller than 50 μm, it is difficult to carry it and it is difficult to provide the coating layer. Further, if the thickness of the porous electrode base material is larger than 350 μm, the handling property is improved, but the electric resistance is increased, so that the power generation performance is deteriorated. If the thickness of the coating layer is smaller than 5 μm, the carbon fibers forming the porous carbon electrode substrate may break through the coating layer and reach the catalyst layer or the electrolyte membrane, which is not preferable. If the thickness is more than 100 μm, the electronic resistance due to the coating layer increases and the power generation performance deteriorates, which is not preferable.

<Roll of gas diffusion layer>
In view of the productivity of the gas diffusion layer and the post-processability, it is preferably a roll-shaped material.
The core material around which the gas diffusion layer is wound is preferably a hollow core material that is lightweight and easy to hold in the unwinding/winding device, and the material is preferably paper or resin. A resin core material is more preferable from the viewpoint of reducing dust generated when the core material is attached to the device. The resin is preferably polyethylene, ABS resin, polystyrene, polypropylene, polyvinyl chloride, polyethylene terephthalate, or the like. Further, it is preferable to use paper as the material from the viewpoint of recycling the core material and from the viewpoint of low cost.

Even with a paper core material, by using a resin-processed core material, it is possible to reduce as much dust as possible when it is attached to the above-mentioned device.

As the core diameter of the core material, the outer diameter thereof is preferably in the range of 84.2 to 182.4 mm from the relationship of the bending radius with respect to the gas diffusion layer. If the outer diameter is less than 84.2 mm, it is close to the maximum radius of curvature of the gas diffusion layer, and the structure change easily occurs before and after winding, which is not preferable. On the other hand, when it is larger than 182.4 mm, the winding diameter becomes too large, which is not preferable because productivity and transportation cost increase. A more preferable range of the outer diameter of the core material is 82.4 to 172.4 mm. When the core material is hollow, the inner diameter of the core material is preferably 76.2 to 152.4 mm, and the thickness of the core material is preferably in the range of 4 to 15 mm. If the thickness of the core material is less than 4 mm, the durability upon repeated use is poor, and if it is more than 15 mm, the weight of the roll-shaped material becomes large, which is not preferable. The core material may be removed after the gas diffusion layer is wound into a roll.

There are two methods for arranging the coating layer in the roll-shaped material, namely, a method of arranging the coating layer inside the roll-shaped material and a method of arranging it outside. Either method can be used in the present invention. When the coating layer is placed inside the roll-shaped material, the porous carbon electrode substrate is placed on the outer layer, which reduces damage to the coating layer due to external shock and winding tightening when the winding length increases. can do. On the other hand, by arranging the coating layer on the outer side of the roll-shaped material, the bending radius of the coating layer becomes large, which is preferable in that damage to the coating layer at the time of winding can be mitigated. Further, by disposing the coating layer on the outer side, it is possible to easily confirm foreign matters attached to the coating layer, coating unevenness, and the like. A protective layer may be provided on the coating layer, that is, between the coating layer and the inner or outer gas diffusion layer. By providing the protective layer, it is possible to prevent scratches and foreign substances such as carbon fibers and carbides that have fallen off from the porous carbon electrode substrate from adhering to the coating layer. Any material that does not adhere to the coating layer may be used as the material of the protective layer, and various release papers and resin films such as polyethylene, ABS resin, polystyrene, polypropylene, polyvinyl chloride, polyethylene terephthalate, and polytetrafluoroethylene may be used. preferable. The thickness of the protective layer is preferably 5 to 100 μm. When the thickness of the protective layer is less than 5 μm, the carbon fiber may be pierced into the protective layer to damage the coating layer, which is not preferable. Further, if the thickness of the protective layer is larger than 100 μm, the protective effect of the coating layer can be expected, but the winding diameter of the roll-shaped material becomes too large, which is not preferable because the productivity is lowered and the transportation cost is increased. The width of the protective layer is equal to or larger than the width of the gas diffusion layer, and the difference is preferably 200 mm or less. When the width is smaller than that of the gas diffusion layer, not only the edge portion of the protective layer damages the coating layer, but the effect of the protective layer cannot be obtained in the portion where the width is insufficient, which is not preferable. Further, if the width of the protective layer is larger than that of the gas diffusion layer and the difference is larger than 200 mm, not only the cost of the protective layer increases but also the balance at the time of winding becomes poor, and as a result, the winding form is not stable. Therefore, it is not preferable.

Various physical property values were measured using the following methods.

<Calculation of porous carbon electrode substrate and coating layer thickness>
From the produced porous carbon electrode substrate and gas diffusion layer, 10 test pieces of 3×3 cm square were randomly taken out, and the thickness of each was measured with a micrometer at 5 points for each sample, and the average thickness was measured. Was calculated and the average thickness of the porous carbon electrode substrate was subtracted from the average thickness of the gas diffusion layer to calculate the thickness of the coating layer.

<Measurement of cracks>
From the produced gas diffusion layer, 10 test pieces of 5×5 mm square were created per 1 m ² , and for each test piece, an accelerating voltage of 5 kV, a spot size of 30 mm, a focal length of 15 mm, and a magnification of 1000 with a scanning electron microscope. The sample was randomly photographed at 10 times and the size and number of cracks were detected. To detect the size and number of cracks, image processing software Image-Pro Plus (manufactured by Nippon Roper Co.) was used for binarization. The size and number of cracks in each sample were determined by the average value.

<Confirmation of changes before and after winding the roll>
The above-mentioned crack measurement was performed even after unwinding the gas diffusion layer wound in a roll shape, and changes in the size and number of cracks were confirmed before and after winding. Those with a rate of change of less than 5% were considered as no change, and those with a rate of change of 5% or more were considered as change. In addition, it was confirmed whether or not carbon fibers were attached to the coating layer.

<Example 1>
(Porous carbon electrode substrate)
As the porous carbon electrode substrate, commercially available carbon paper or carbon cloth can be used, but in the present invention, the porous carbon electrode substrate was manufactured in order to obtain a smooth porous carbon electrode substrate.

As the carbon fiber (A), a PAN-based carbon fiber having an average fiber diameter of 7 μm and an average fiber length of 3 mm was prepared. Further, as the carbon fiber precursor fiber (b), an acrylic fiber having an average fiber diameter of 4 μm and an average fiber length of 3 mm (Mitsubishi Rayon Co., Ltd., trade name: D122), fibrillar fiber (b′), beaten Easily splittable acrylic sea-island composite fiber composed of acrylic polymer and diacetate (cellulose acetate) that are fibrillated by Mitsubishi Rayon Co., Ltd., trade name: Bonnell MVP-C651, average fiber length : 3 mm) was prepared.

A gas diffusion layer was manufactured by the following operations <1> to <10>.

<1> Disaggregation of carbon fiber (A) Carbon fiber (A) is dispersed in water so that the fiber concentration is 1% (10 g/L), and disaggregated through a mixer to form disaggregated slurry fiber (SA). did.

<2> Disaggregation of carbon fiber precursor fiber (b) Carbon fiber precursor fiber (b) is dispersed in water so that the fiber concentration is 1% (10 g/L), and disaggregated through a mixer to disaggregate. The slurry fiber (Sb) was used.

<3> Disaggregation of fibrillar fibers (b′) The easily splittable acrylic sea-island composite fibers are dispersed in water so that the fiber concentration is 1% (10 g/L), and beaten and disaggregated through a mixer, The disaggregated slurry fiber (Sb') was used.

<4> Production of papermaking body Carbon fiber (A), carbon fiber precursor fiber (b) and fibrillar fiber (b') have a mass ratio of 70:10:20, and the fiber concentration in the slurry is The disaggregated slurry fibers (SA), the disaggregated slurry fibers (Sb), the disaggregated slurry fibers (Sb'), and the dilution water were weighed and dispersed so as to be 1.44 g/L. For the papermaking, a net drive unit and a sheet-like material conveying device composed of a net which is 60 cm wide x 585 cm long and made of a plastic net plain weave mesh which is continuously rotated by connecting it in a belt shape, the width of the slurry supply part is 48 cm, and the lower part of the net. A processing apparatus comprising a reduced pressure dehydration apparatus arranged in the above was used. A pressurized water jet injection treatment device equipped with the following three water jet nozzles was arranged downstream of the treatment device.

Nozzle 1: Hole diameter φ0.15 mm x 501 holes
Width hole pitch 1mm (1001 hole/width 1m)
1 row arrangement, nozzle effective width 500mm

Nozzle 2: Hole diameter φ0.15 mm x 501 holes
Width hole pitch 1mm (1001 holes/width 1m)
1 row arrangement, nozzle effective width 500mm

Nozzle 3: Hole diameter φ0.15 mm x 1002 holes
Width hole pitch 1.5mm
3 rows arrangement, pitch between rows 5mm, effective nozzle width 500mm

With the pressurized water jet pressure set to 1 MPa nozzle 1, pressure 2 MPa (nozzle 2), pressure 1 MPa (nozzle 3), the slurry in which the fibers are dispersed is charged from the slurry supply unit, and after decompression dehydration, nozzle 1, nozzle 2, nozzle The paper was passed through in the order of 3 and subjected to the entanglement treatment to obtain a paper body having a three-dimensional entangled structure. The papermaking body was dried at 150° C. for 3 minutes with a pin tenter tester (PT-2A-400 manufactured by Tsujii Dyeing Machine Co., Ltd.) to obtain a papermaking body. The dispersed state of the carbon fibers (A), the carbon fiber precursor fibers (b), and the fibrillar fibers (b′) in the papermaking body was good, and the handleability was good.

<5> Resin Impregnation/Drying The obtained papermaking body was impregnated with a phenol resin dispersion and dried at an ambient temperature of 100° C. using a hot air dryer.

<6> Pressurizing and Heat-Molding Next, both sides of the papermaking body are arranged so as to be sandwiched between papers coated with a silicone-based release agent, and a double belt press machine is operated at 190° C. and a belt speed of 0.2 m/min. And press-molded.

<7> Carbonization treatment After that, this precursor sheet was carbonized in a carbonization furnace in a nitrogen gas atmosphere at 2000° C. to obtain a porous carbon electrode substrate. The obtained porous carbon electrode substrate was smooth without warping or waviness. The thickness of the obtained porous carbon electrode substrate was 155 μm.

<8> Preparation of coating liquid 1 Denka Black (manufactured by Denki Kagaku Kogyo Co., Ltd.), ion-exchanged water, and isopropyl alcohol were mixed at a ratio of 5:100:80, and a homomixer MARK-II (manufactured by Primix Co., Ltd.) was used. Then, stirring was performed at 15000 rpm for 30 minutes while cooling to obtain a coating liquid 1.

<9> Preparation of coating liquid 2 Polytetrafluoroethylene (PTFE) dispersion was added to coating liquid 1 at a ratio of 0.3 to carbon black 1, and the dispersion was stirred at 500 rpm for 5 minutes to prepare coating liquid 1. Got 2.

<10> Preparation of Water Repellent Treatment Liquid for Porous Carbon Electrode Base Material To prepare a water repellent treatment liquid for porous carbon electrode base material, PTFE dispersion (31-JR, manufactured by Mitsui DuPont Fluorochemical) and an interface were used. An activator (polyoxyethylene (10) octyl phenyl ether) and distilled water were used. After adjusting the solid content concentration in the water repellent treatment solution to be 1 wt% for PTFE and 2 wt% for the surfactant, distilled water was added, and the water repellency was obtained by stirring with a disper at 1000 rpm for 10 minutes. A processing solution was prepared.

<11> Water-repellent treatment on porous carbon electrode substrate A porous carbon electrode substrate was impregnated by immersing it in the above water-repellent treatment liquid. Excessive water repellent treatment adhered to the porous carbon electrode substrate by pressing the impregnated porous carbon electrode substrate against the bar, removing excess water repellent treatment liquid, and then conveying at a speed of 2 m/min. The liquid was removed and the porous carbon electrode substrate was heat-treated in a heat treatment furnace to obtain a water repellent porous carbon electrode substrate.

<12> Formation of coating layer Further, the coating liquid 2 was applied onto the porous carbon electrode substrate with a target thickness of 10 µm, and then dried for 20 minutes using a hot air drying oven set at 150°C. Further, after drying, sintering treatment was performed in a sintering furnace at 360° C. for 1 hour to obtain a gas diffusion layer having a coating layer formed thereon. The number of cracks formed in the coating layer of the obtained gas diffusion layer was 0.019 mm, and the number of 0.11 μm wide cracks was 34/m ² . The obtained gas diffusion layer was wound on a paper core having an inner diameter of 76.2 mm, a thickness of 4 mm, and an outer diameter of 84.2 mm so that the coating layer was always on the inner side, and it was wound in a good form. I was able to. When the roll was rewound and a crack was confirmed, the change was less than 5%. Further, the adhesion of carbon fibers to the coating layer was also small. The results are summarized in Table 1.

<Example 2>
A gas diffusion layer was obtained in the same manner as in Example 1 except that the thickness of the porous carbon electrode base material was 78 μm, the drying temperature of the coating layer was 200° C., and the target thickness of the coating layer was 30 μm. The cracks formed in the coating layer of the obtained gas diffusion layer had a length of 0.021 mm and a width of 0.25 μm and the number of cracks was 511/m ² . The obtained gas diffusion layer was wound on a polyethylene core material having an inner diameter of 152.4 mm, a thickness of 4 mm and an outer diameter of 160.4 mm so that the coating layer was always on the outer side. I was able to. When the roll was rewound and a crack was confirmed, the change was less than 5%. Further, the adhesion of carbon fibers to the coating layer was also small. The results are summarized in Table 1.

<Example 3>
A gas diffusion layer was obtained in the same manner as in Example 1 except that the thickness of the porous carbon electrode substrate was 201 μm, the drying temperature of the coating layer was 300° C., and the target thickness of the coating layer was 50 μm. The cracks formed in the coating layer of the obtained gas diffusion layer had a length of 0.025 mm and a width of 0.30 μm and the number was 777/m ² . The obtained gas diffusion layer was wound on a polyvinyl chloride core material having an inner diameter of 76.2 mm, a thickness of 4 mm and an outer diameter of 84.2 mm so that the coating layer was always on the outer side. I was able to take it. When the roll was rewound and a crack was confirmed, the change was less than 5%. Further, the adhesion of carbon fibers to the coating layer was also small. The results are summarized in Table 1.

<Example 4>
The thickness of the porous carbon electrode substrate is 144 μm, the plate heater is used to dry the coating layer, and the temperature of the heating surface is set to 150° C., and the surface without the coating layer is in contact with the heating surface. A gas diffusion layer was obtained in the same manner as in Example 1 except that the drying was performed. The cracks formed in the coating layer of the obtained gas diffusion layer were 0.444 mm in length and 4.5 μm in width, and the number of cracks was 33/m ² . The obtained gas diffusion layer was placed on a polyvinyl chloride core having an inner diameter of 76.2 mm, a thickness of 15 mm, and an outer diameter of 106.2 mm so that the coating layer was always on the inner side of the roll-shaped material, and as a protective film for the coating layer. A film made of polypropylene (PP) having a thickness of 25 μm was wound so that the film was arranged between the respective layers of the gas diffusion layer so as to protect the coating layer over the entire width, and the film was wound in a good form. It was When the roll was rewound and a crack was confirmed, the change was less than 5%. Further, the adhesion of carbon fibers to the coating layer was also small. The results are summarized in Table 1.

<Example 5>
The thickness of the porous carbon electrode base material is 82 μm, the plate heater is used to dry the coating layer, and the temperature of the heating surface is set to 200° C., and the surface without the coating layer is brought into contact with the heating surface. A gas diffusion layer was obtained in the same manner as in Example 2 except that the drying was performed. The length of the cracks formed in the coating layer of the obtained gas diffusion layer was 0.812 mm, and the number of 2.1 μm wide cracks was 311/m ² . The obtained gas diffusion layer was wound around a polyethylene core material having an inner diameter of 152.4 mm, a thickness of 15 mm and an outer diameter of 182.4 mm so that the coating layer was always on the inner side. did it. When the roll was rewound and a crack was confirmed, the change was less than 5%. Further, the adhesion of carbon fibers to the coating layer was also small. The results are summarized in Table 1.

<Example 6>
The thickness of the porous carbon electrode base material is 210 μm, the plate heater is used to dry the coating layer, and the temperature of the heating surface is set to 300° C., and the surface without the coating layer is brought into contact with the heating surface. A gas diffusion layer was obtained in the same manner as in Example 3 except that the drying was performed. The number of cracks formed in the coating layer of the obtained gas diffusion layer was 0.914 mm in length and the number of 1.8 μm in width was 741 pieces/m ² . The obtained gas diffusion layer was placed on a paper core having an inner diameter of 76.2 mm, a thickness of 4 mm, and an outer diameter of 84.2 mm so that the coating layer was always on the outer side of the roll-shaped material, and the thickness was used as a protective film for the coating layer. When a film made of 50 μm polypropylene (PP) was wound so that the film was arranged between the respective layers of the gas diffusion layer so as to protect the coating layer over the entire width, the film was able to be wound in a good form. When the roll was rewound and a crack was confirmed, the change was less than 5%. Further, the adhesion of carbon fibers to the coating layer was also small. The results are summarized in Table 1.

<Example 7>
The thickness of the porous carbon electrode substrate is set to 148 μm, a heating roll is used to dry the coating layer, and the temperature of the heating surface is set to 150° C., and the surface on which the coating layer is not formed contacts the heating surface. A gas diffusion layer was obtained in the same manner as in Example 1 except that the drying was performed. The number of cracks formed in the coating layer of the obtained gas diffusion layer was 0.714 mm in length and the number of 2.2 μm in width was 35/m ² . The obtained gas diffusion layer was wound around a polyvinyl chloride core material having an inner diameter of 152.4 mm, a thickness of 15 mm and an outer diameter of 182.4 mm so that the coating layer was always on the inner side, and was wound in a good form. I was able to. When the roll was rewound and a crack was confirmed, the change was less than 5%. Further, the adhesion of carbon fibers to the coating layer was also small. The results are summarized in Table 1.

<Example 8>
The thickness of the porous carbon electrode substrate is 84 μm, the heating layer is used to dry the coating layer, the temperature of the heating surface is set to 200° C., and the surface without the coating layer is brought into contact with the heating surface. A gas diffusion layer was obtained in the same manner as in Example 2 except that the drying was performed. The cracks formed in the coating layer of the obtained gas diffusion layer had a length of 0.623 mm and a width of 2.1 μm and the number of cracks was 256/m ² . The obtained gas diffusion layer was wound on a polypropylene core material having an inner diameter of 76.2 mm, a thickness of 4 mm and an outer diameter of 84.2 mm so that the coating layer was always on the outer side. did it. When the roll was rewound and a crack was confirmed, the change was less than 5%. Further, the adhesion of carbon fibers to the coating layer was also small. The results are summarized in Table 1.

<Example 9>
The thickness of the porous carbon electrode substrate is set to 202 μm, a heating roll is used to dry the coating layer, and the temperature of the heating surface is set to 300° C., and the surface without the coating layer is brought into contact with the heating surface. A gas diffusion layer was obtained in the same manner as in Example 3 except that the drying was performed. The number of cracks formed in the coating layer of the obtained gas diffusion layer was 0.412 mm in length and 1.3 μm in width, and the number was 711/m ² . The obtained gas diffusion layer was wound around a polyethylene core material having an inner diameter of 152.4 mm, a thickness of 15 mm and an outer diameter of 182.4 mm so that the coating layer was always on the inner side. did it. When the roll was rewound and a crack was confirmed, the change was less than 5%. Further, the adhesion of carbon fibers to the coating layer was also small. The results are summarized in Table 1.

<Example 10>
The thickness of the porous carbon electrode substrate was set to 148 μm, an infrared oven was used to dry the coating layer, and the temperature of the porous carbon electrode substrate and coating layer to be heated was set to 150° C. and dried. A gas diffusion layer was obtained in the same manner as in Example 1 except for the above. The cracks formed in the coating layer of the obtained gas diffusion layer had a length of 0.049 mm and a width of 7.7 μm and the number was 28/m 2. The obtained gas diffusion layer was placed on a polyvinyl chloride core material having an inner diameter of 152.4 mm, a thickness of 15 mm, and an outer diameter of 182.4 mm so that the coating layer was always on the outer side of the roll-shaped material, and as a protective film for the coating layer, A film made of polyethylene terephthalate (PET) having a thickness of 25 μm was wound so that the film was arranged between the layers of the gas diffusion layer so as to protect the coating layer over the entire width, and the film was wound in a good shape. It was When wound up, it could be wound up in a good form. When the roll was rewound and a crack was confirmed, the change was less than 5%. Further, the adhesion of carbon fibers to the coating layer was also small. The results are summarized in Table 1.

<Example 11>
The thickness of the porous carbon electrode substrate was set to 74 μm, an infrared oven was used to dry the coating layer, and the temperature of the heated porous carbon electrode substrate and the coating layer was set to 200° C. and dried. A gas diffusion layer was obtained in the same manner as in Example 2 except for the above. The cracks formed in the coating layer of the obtained gas diffusion layer had a length of 0.088 mm and a width of 8.8 μm and the number thereof was 511/m ² . The obtained gas diffusion layer was wound on a paper-made core material having an inner diameter of 76.2 mm, a thickness of 4 mm and an outer diameter of 84.2 mm so that the coating layer was always on the inner side. did it. When the roll was rewound and a crack was confirmed, the change was less than 5%. Further, the adhesion of carbon fibers to the coating layer was also small. The results are summarized in Table 1.

<Example 12>
The thickness of the porous carbon electrode substrate was set to 188 μm, an infrared oven was used to dry the coating layer, and the temperature of the porous carbon electrode substrate and the coating layer to be heated were set to 300° C. and dried. A gas diffusion layer was obtained in the same manner as in Example 3 except for the above. The cracks formed in the coating layer of the obtained gas diffusion layer had a length of 0.021 mm and a width of 6.6 μm and the number of cracks was 684/m ² . The obtained gas diffusion layer was placed on a polypropylene core material having an inner diameter of 152.4 mm, a thickness of 15 mm, and an outer diameter of 182.4 mm, so that the coating layer was always on the outer side of the roll-shaped material, and a protective film of the coating layer had a thickness of 50 μm. When a film made of polyethylene terephthalate (PET) of 1 was wound so that the film was arranged between the respective layers of the gas diffusion layer so as to protect the coating layer over the entire width, the film could be wound in a good form. When wound up, it could be wound up in a good form. When the roll was rewound and a crack was confirmed, the change was less than 5%. Further, the adhesion of carbon fibers to the coating layer was also small. The results are summarized in Table 1.

<Comparative Example 1>
The thickness of the porous carbon electrode base material was 81 μm, the coating layer was dried using an infrared oven, and the temperature of the heated porous carbon electrode base material and the coating layer was set to 100° C. and dried. A gas diffusion layer was obtained in the same manner as in Example 2 except for the above. The number of cracks formed in the coating layer of the obtained gas diffusion layer was 0.0008 mm and the number of cracks was 0.15 μm in width was 104/m ² . The obtained gas diffusion layer was placed on a paper core material having an inner diameter of 152.4 mm, a thickness of 15 mm, and an outer diameter of 182.4 mm so that the coating layer was always on the inner side of the roll-shaped material, and a protective film of the coating layer had a thickness of 50 μm. A film made of polyethylene terephthalate (PET) was wound so that the film was arranged between the respective layers of the gas diffusion layer so as to protect the coating layer over the entire width. When the roll-shaped material was rewound and cracks were confirmed, the length and number of cracks significantly increased, and the change exceeded 5%, which was unsatisfactory. Further, the adhesion of carbon fibers to the coating layer was partially seen. The results are summarized in Table 1.

<Comparative example 2>
The thickness of the porous carbon electrode substrate was set to 91 μm, an infrared oven was used to dry the coating layer, and the temperature of the heated porous carbon electrode substrate and coating layer was set to 350° C. and dried. A gas diffusion layer was obtained in the same manner as in Example 2 except for the above. The number of cracks formed in the coating layer of the obtained gas diffusion layer was 1.5 mm in length and 8.5 μm in width, and the number was 28/m ² . The obtained gas diffusion layer was placed on a polyethylene core material having an inner diameter of 152.4 mm, a thickness of 15 mm and an outer diameter of 182.4 mm so that the coating layer was always on the outer side of the roll-shaped material, and a protective film for the coating layer had a thickness of 50 μm. A film made of polyethylene terephthalate (PET) was wound so that the film was arranged between the respective layers of the gas diffusion layer so as to protect the coating layer over the entire width. When the roll-shaped product was rewound and a crack was confirmed, the length, width, and number of the crack were significantly increased, and the change exceeded 5%, which was a defect. Further, the adhesion of carbon fibers to the coating layer was partially seen. The results are summarized in Table 1.

<Comparative example 3>
The thickness of the porous carbon electrode substrate is set to 77 μm, a heating roll is used to dry the coating layer, and the temperature of the heating surface is set to 50° C., and the surface without the coating layer is brought into contact with the heating surface. A gas diffusion layer was obtained in the same manner as in Example 2 except that the drying was performed. The cracks formed in the coating layer of the obtained gas diffusion layer had a length of 0.028 mm and a width of 0.02 μm of 311 cracks/m ² . The obtained gas diffusion layer was placed on a polyvinyl chloride core material having an inner diameter of 152.4 mm, a thickness of 15 mm, and an outer diameter of 182.4 mm so that the coating layer was always on the inner side of the roll-shaped material, and as a protective film for the coating layer, A film made of polyethylene terephthalate (PET) having a thickness of 50 μm was wound so that the film was arranged between the respective layers of the gas diffusion layer so as to protect the coating layer over the entire width. When the roll-shaped product was rewound and a crack was confirmed, the length, width, and number of the crack were significantly increased, and the change exceeded 5%, which was a defect. Further, the adhesion of carbon fibers to the coating layer was partially seen. The results are summarized in Table 1.

<Comparative example 4>
The thickness of the porous carbon electrode base material is 74 μm, the heating roll is used to dry the coating layer, and the temperature of the heating surface is set to 350° C., and the surface without the coating layer is brought into contact with the heating surface. A gas diffusion layer was obtained in the same manner as in Example 2 except that the drying was performed. The cracks formed in the coating layer of the obtained gas diffusion layer had a length of 0.040 mm and a width of 16 μm, and the number of cracks was 35/m ² . The obtained gas diffusion layer was placed on a polypropylene core material having an inner diameter of 152.4 mm, a thickness of 15 mm, and an outer diameter of 182.4 mm so that the coating layer was always on the outer side of the roll-like material, and a protective film of the coating layer had a thickness of 50 μm. A film made of polyethylene terephthalate (PET) was wound so that the film was arranged between the respective layers of the gas diffusion layer so as to protect the coating layer over the entire width. When the roll-shaped product was rewound and a crack was confirmed, the length, width, and number of the crack were significantly increased, and the change exceeded 5%, which was a defect. Further, the adhesion of carbon fibers to the coating layer was partially seen. The results are summarized in Table 1.

<Comparative Example 5>
A gas diffusion layer was obtained in the same manner as in Example 2 except that the thickness of the porous carbon electrode substrate was set to 75 μm and the drying temperature of the coating layer was set to 50° C. The number of cracks formed in the coating layer of the obtained gas diffusion layer was 0.049 mm in length and the number of 5.1 μm in width was 15/m ² . The obtained gas diffusion layer was placed on a paper core material having an inner diameter of 152.4 mm, a thickness of 15 mm, and an outer diameter of 182.4 mm so that the coating layer was always on the inner side of the roll-shaped material, and a protective film of the coating layer had a thickness of 50 μm. A film made of polyethylene terephthalate (PET) was wound so that the film was arranged between the respective layers of the gas diffusion layer so as to protect the coating layer over the entire width. When the roll-shaped product was rewound and a crack was confirmed, the length, width, and number of the crack were significantly increased, and the change exceeded 5%, which was a defect. Further, the adhesion of carbon fibers to the coating layer was partially seen. The results are summarized in Table 1.

<Comparative example 6>
A gas diffusion layer was obtained in the same manner as in Example 2 except that the thickness of the porous carbon electrode substrate was 81 μm and the drying temperature of the coating layer was set to 350° C. The cracks formed in the coating layer of the obtained gas diffusion layer had a length of 0.485 mm and a width of 2.1 μm and the number of cracks was 1210/m ² . The obtained gas diffusion layer was placed on a paper core material having an inner diameter of 152.4 mm, a thickness of 15 mm, and an outer diameter of 182.4 mm so that the coating layer was always on the outer side of the roll-like material, and a protective film of the coating layer had a thickness of 50 μm. A film made of polyethylene terephthalate (PET) was wound so that the film was arranged between the respective layers of the gas diffusion layer so as to protect the coating layer over the entire width. When the roll-shaped material was rewound and cracks were confirmed, the coating layer peeled off when unwound, and the length, width, and number of cracks significantly increased, and the change exceeded 5%, which was a defect. Met. Further, the adhesion of carbon fibers to the coating layer was partially seen. The results are summarized in Table 1.

<Comparative Example 7>
A gas diffusion layer was obtained in the same manner as in Example 1 except that the thickness of the porous carbon electrode substrate was 81 μm and the coating layer was set to be naturally dried in the air. The cracks formed in the coating layer of the obtained gas diffusion layer had a length of 0.0008 mm and a width of 0.03 μm and the number of cracks was 11/m ² . The obtained gas diffusion layer was placed on a paper core material having an inner diameter of 152.4 mm, a thickness of 15 mm, and an outer diameter of 182.4 mm so that the coating layer was always on the inner side of the roll-shaped material, and a protective film of the coating layer had a thickness of 50 μm. A film made of polyethylene terephthalate (PET) was wound so that the film was arranged between the respective layers of the gas diffusion layer so as to protect the coating layer over the entire width. When the roll-shaped product was rewound and a crack was confirmed, the length, width, and number of the crack were significantly increased, and the change exceeded 5%, which was a defect. Further, the adhesion of carbon fibers to the coating layer was partially seen. The results are summarized in Table 1.

<Comparative Example 8>
The thickness of the porous carbon electrode substrate is set to 78 μm, the plate heater is used to dry the coating layer, and the temperature of the heating surface is set to 350° C., and the surface without the coating layer is brought into contact with the heating surface. A gas diffusion layer was obtained in the same manner as in Example 1 except that the drying was performed. The cracks formed in the coating layer of the obtained gas diffusion layer had a length of 1.4 mm and a number of 15 μm in width of 1450/m ² . The obtained gas diffusion layer was placed on a paper core material having an inner diameter of 152.4 mm, a thickness of 15 mm, and an outer diameter of 182.4 mm so that the coating layer was always on the inner side of the roll-shaped material, and a protective film of the coating layer had a thickness of 50 μm. A film made of polyethylene terephthalate (PET) was wound so that the film was arranged between the respective layers of the gas diffusion layer so as to protect the coating layer over the entire width. When the roll-shaped material was rewound and cracks were confirmed, the coating layer peeled off when unwound, and the length, width, and number of cracks significantly increased, and the change exceeded 5%, which was a defect. Met. Further, the adhesion of carbon fibers to the coating layer was partially seen. The results are summarized in Table 1.

Claims (8)

25 to 1,000 cracks/m on the surface of at least one surface of the porous carbon electrode base material, which are composed of carbon particles and a water repellent and have a length of 0.001 to 1 mm and a width of 0.05 to 10 μm.
A gas diffusion layer provided with a coating layer having ² . The gas diffusion layer according to claim 1, wherein the porous electrode substrate constituting the gas diffusion layer has a thickness of 50 to 250 µm, and the coating layer formed on at least one surface has a thickness of 5 to 100 µm. A roll-shaped product of the gas diffusion layer, wherein the gas diffusion layer according to claim 1 or 2 is wound around a core material having an outer diameter of 84.2 to 167.4 mm in a roll shape. The roll-shaped product of the gas diffusion layer according to claim 3, wherein the gas diffusion layer is wound so that the coating layer is arranged outside the porous carbon electrode substrate with respect to the core material. The roll-shaped material of the gas diffusion layer according to claim 3, wherein the gas diffusion layer is wound so that the coating layer is arranged inside the porous carbon electrode substrate with respect to the core material. The roll-shaped material of the gas diffusion layer according to any one of claims 3 to 5, wherein the core material is paper. The roll-shaped material of the gas diffusion layer according to claim 3, wherein the material of the core material is a resin. A protective layer having a thickness of 5 to 100 μm is wound around the core together with the gas diffusion layer.
7. The roll-shaped material of the gas diffusion layer according to any one of 7 above .