JP2014135270A - Porous carbon electrode and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous carbon electrode for a solid polymer fuel cell, which can be manufactured by a simple method and nonetheless has high peel strength of a coating layer with regard to a gas diffusion electrode base material.SOLUTION: A method of manufacturing a porous carbon electrode, includes the following steps from (1) to (4): a step (1) of impregnating a porous carbon electrode base material with a solution containing a water repellent and a surface active surfactant, the porous carbon electrode base material having a carbon short fiber bonded by a carbon; a step (2) of applying a coating liquid comprising a carbon powder and the water repellent onto the porous carbon electrode base material which is impregnated with the solution containing the water repellent and the surface active surfactant, thereby forming a uniformed coating film; a step (3) of drying the coating film of the porous carbon electrode base material having the coating film formed thereon, under an atmosphere of 50 to 200°C; and a step (4) of calcinating the porous carbon electrode base material having the dried coating film formed thereon, under an atmosphere of 300 to 400°C.

Description

  The present invention relates to a porous carbon electrode used for a polymer electrolyte fuel cell and a method for producing the same.

  A polymer electrolyte fuel cell is an apparatus 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 a hydrogen ion (proton). And a polymer electrolyte membrane that selectively conducts. Further, two sets of gas diffusion electrodes each having a catalyst layer mainly composed of carbon powder carrying a noble metal catalyst and a gas diffusion electrode substrate are joined to both surfaces of the polymer electrolyte membrane.

  Such a joined body composed of a polymer electrolyte membrane and two sets of gas diffusion electrodes is called a membrane-electrode assembly (MEA). Further, on both outer sides of the MEA, separators are provided in which gas flow paths for supplying fuel gas or oxidizing gas and for discharging generated gas and excess gas are formed.

  The gas diffusion electrode substrate is mainly required to have the following three functions. The first function is a function of uniformly supplying 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 disposed outside the first function. The second function is a function of discharging 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 having a porous structure made of a carbonaceous material is usually used. Specifically, substrates using carbon fibers such as carbon paper, carbon fiber cloth, carbon fiber felt, etc. are generally used. These base materials are not only highly conductive due to carbon fibers, but are porous materials, and are therefore suitable materials for gas diffusion layers because of high permeability of liquids such as fuel gas and generated water.

  For the purpose of reducing the contact resistance between the porous carbon electrode substrate such as carbon paper and carbon cloth mentioned above and the electrode catalyst layer, and efficiently discharging generated water generated during power generation, carbon fine particles and water repellent A coating layer made of may be provided between the porous carbon electrode substrate and the electrode catalyst layer. In general, from the viewpoint of drainage, the gas diffusion electrode substrate itself is generally treated to increase the water repellency, and the gas diffusion electrode substrate is impregnated with a fluorine compound solution and dried. There is a method of sintering after heating. In addition, when water repellent treatment of the gas diffusion layer base material is performed, the sintering process in the water repellent treatment of the gas diffusion electrode base material is performed by applying and drying the ink that becomes the microporous layer after performing the drying treatment. A manufacturing method that eliminates the above has been disclosed. However, the conventional method requires a heat treatment furnace for drying the water repellent, which increases the cost, and heat is applied in the drying step, resulting in uneven adhesion of the water repellent, resulting in gas The problem that the peeling strength of the coating layer with respect to a diffusion electrode base material will fall has arisen.

Japanese Patent No. 3382213

  The present invention overcomes the above problems and provides a porous carbon electrode for a polymer electrolyte fuel cell having a high peel strength of a coating layer on a gas diffusion electrode substrate while being a simple manufacturing method. For the purpose.

  Specifically, the above problems are solved by the following inventions (1) to (5).

(1) A method for producing a porous carbon electrode, comprising the following steps [1] to [4].
Step [1]: A step of impregnating a porous carbon electrode base material in which short carbon fibers are bound with carbon with a solution containing a water repellent and a surfactant.
Step [2]: A coating solution composed of carbon powder and a water repellent agent is applied onto a porous carbon electrode substrate impregnated with a solution containing a water repellent agent and a surfactant to form a uniform coating film. Process.
Step [3]: A step of drying the porous carbon electrode substrate on which the coating film is formed in an environment of 50 to 200 ° C.
Step [4]: A step of producing a porous carbon electrode by firing the porous carbon electrode substrate on which the dried coating film has been formed in an environment of 300 to 400 ° C.

  (2) The production method according to (1), wherein the surfactant is polyoxyethylene (10) octylphenyl ether, and the concentration is 0.1 to 5 wt% or less.

  (3) A porous carbon electrode produced by the method of (1) or (2) above.

  (4) A porous carbon electrode in which a coating layer composed of carbon powder and a water repellent is formed on one surface of a porous carbon electrode base material in which short carbon fibers are bound by carbon, and the surface pressure The electrical resistance in the perpendicular direction when 0.5 MPa is applied is greater than 0.60 Ω · cm and less than or equal to 0.8 Ω · cm, and between the porous carbon electrode substrate and the coating layer obtained by the following peel test A porous carbon electrode having a peeling degree of less than 50%.

<Peel test>
Tape: Nichiban Sealing Masking Tape No. 252
Size of test piece: 5 x 5 cm
Test Method: A tape cut to 3 × 3 cm is attached to the coating layer of the test piece, a load of 10 g / cm ² is applied to the adhesive surface for 30 seconds, and then the tape is peeled off. The area of the coating layer peeled off from the test piece and adhered to the tape is measured.

  Measure the area of the coating layer peeled off from the test piece and attached to the tape: The image of the tape surface to which the coating layer peeled off from the test piece was attached using a digital camera, the aspect ratio was 4: 3, and the number of recording pixels was 3648 × Shoot as 2736 pixels. Using the image analysis software Image-Pro Plus (manufactured by Nippon Roper) on the obtained image, the area of the coating layer having an area of 100 × 100 μm or more is measured, and the ratio to the tape area is calculated. The test is performed three times for one sample, and the degree of peeling is determined by the average value.

  (5) The porous carbon electrode according to the above (4), wherein a coating layer composed of carbon powder and a water repellent is formed on the side where the surface of the porous carbon electrode substrate is rough.

  Although it is a simple manufacturing method, a porous carbon electrode for a polymer electrolyte fuel cell having a high peel strength of a coating layer with respect to a gas diffusion electrode substrate can be provided.

It is a scanning electron micrograph of the porous carbon electrode surface of this invention.

  Hereinafter, the present invention will be described in detail.

1. Production method of porous carbon electrode The porous carbon electrode of the present invention can be produced by a production method including the following steps [1] to [4].
Step [1]: A step of impregnating a porous carbon electrode base material in which short carbon fibers are bound with carbon with a solution containing a water repellent and a surfactant.
Step [2]: A coating solution composed of carbon powder and a water repellent agent is applied onto a porous carbon electrode substrate impregnated with a solution containing a water repellent agent and a surfactant to form a uniform coating film. Process.
Step [3]: A step of drying the porous carbon electrode substrate on which the coating film is formed in an environment of 50 to 200 ° C.
Step [4]: A step of producing a porous carbon electrode by firing the porous carbon electrode substrate on which the dried coating film has been formed in an environment of 300 to 400 ° C.

<Treatment of porous carbon electrode substrate>
In the water repellent treatment performed to impart water repellency to the porous carbon electrode substrate, a dispersion liquid in which particles of a water repellent such as a fluororesin are dispersed in a solvent is used. When water is used as the solvent, the water repellent is not dispersed in water as it is, and is thus dispersed in water with an appropriate surfactant. Further, as the dispersion, a dispersion in which a water repellent is dispersed in advance can be used. As a conventional water repellent treatment procedure, a porous carbon electrode substrate is impregnated by an existing spray method or immersion method using a dispersion of a water repellent and a surfactant, and then subjected to an optional heat treatment. It was customary to perform drying and sintering treatments. However, the conventional treatment method has a high cost due to heat treatment, causing uneven adhesion of the water repellent to the substrate, and tends to reduce the peel strength of the coating layer on the porous carbon electrode substrate. Therefore, in the present invention, the heat treatment step in the water repellent treatment step that causes uneven adhesion of the water repellent to the porous carbon electrode substrate is omitted.

<Step [1]: A step of impregnating a porous carbon electrode base material in which short carbon fibers are bound with carbon with a solution containing a water repellent and a surfactant>
Examples of the water repellent include a 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 dispersed in advance may be used. The concentration of the water repellent is preferably 1 to 30 wt%, more preferably 2 to 20 wt% in terms of weight concentration in order to ensure the water repellency of the porous carbon electrode substrate.

  A known surfactant can be used for dispersing the water repellent in water and controlling the wettability of the porous carbon electrode substrate. Examples thereof include nonionic surfactants such as polyoxyethylene (10) octylphenyl ether (for example, Triton X-100 manufactured by ACROS ORGANICS), alkyl ether, alkylphenyl ether, and the like. From the viewpoint of handleability and decomposition temperature, it is preferable to use polyoxyethylene (10) octylphenyl ether. The concentration is preferably 0.1 to 10 wt%, more preferably 0.1 to 5.0 wt% in view of wettability control and decomposition time.

  As the impregnation method, for example, a known technique such as a dip nip method, a kiss coating method, a spray method, or a curtain coating method can be used.

The water content in the porous carbon electrode substrate after impregnation is 100 to 500% with respect to the weight of the untreated porous carbon electrode substrate in view of the coating property and handling property of the coating liquid in the subsequent step. It is preferable that it is 200% to 400%. Such moisture content is calculated by measuring the weight of the porous carbon electrode substrate before and after the impregnation treatment.
<Step [2]: Applying a coating liquid composed of carbon powder and a water repellent on a porous carbon electrode substrate impregnated with a solution containing a water repellent and a surfactant to form a uniform coating film Process to make>
The solvent of the coating liquid composed of carbon powder and a water repellent is composed of an aqueous system or a mixed solvent of an organic solvent and water or an organic solvent. The ratio of the carbon powder and the water repellent is 5 to 100 parts by weight, preferably 10 to 50 parts by weight, based on 100 parts by weight of the carbon powder.

  The coating liquid can be obtained by preparing and mixing a carbon powder dispersion and a water repellent dispersion, respectively. In order to obtain the carbon dispersion, water is mixed into 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. Such organic solvents are preferably lower alcohols and acetone. Examples of the surfactant include polyoxyethylene (10) octylphenyl ether (for example, Triton X-100 manufactured by ACROS ORGANICS), alkyl ether, alkylphenyl ether, and the like. The addition amount of the surfactant may be 0.1 wt% or more with respect to the entire coating liquid in order to increase the dispersibility of the carbon powder, and if the addition amount is too large, foaming occurs, so that 5 wt%. The following is preferable.

  As the carbon powder to be used, 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), etc. are used as carbon black. Can be used. From the viewpoint of developing higher conductivity, carbon black is preferable.

  The primary particle size of carbon black to be used may be in a range that does not impair the effects of the present invention, but is preferably 20 to 80 nm. The water repellent is, for example, a 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 using a surfactant, or a dispersion dispersed in advance may be used.

<< Formation of coating film >>
As a coating method for forming a coating liquid for forming a coating film on a 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, Examples include curtain coating and roll coating. By these methods, a uniform coating film can be formed on the porous carbon electrode substrate.

<Process [3]: The process of drying a coating film in the environment of 50-200 degreeC in the porous carbon electrode base material in which the coating film was formed>
In the present invention, the porous carbon electrode substrate on which the coating film is formed is placed in an environment of 50 to 200 ° C. to dry the coating film. For example, an environment of 50 to 200 ° C. can be created using a hot air dryer or an IR heater.

  The atmospheric temperature at the time of drying is preferably in the range of 50 to 200 ° C., more preferably 70 to 150 ° C., in order to prevent cracking due to the drying rate and aggregation of the coating film. In consideration of productivity, the time is preferably 5 minutes to 20 minutes, more preferably 7 to 15 minutes.

<Step [4]: A step of producing a porous carbon electrode by firing a porous carbon electrode substrate on which a coating film after drying is formed in an environment of 300 to 400 ° C.>
In this invention, a porous carbon electrode is manufactured by baking the "porous carbon electrode base material in which the coating film was formed" after drying in 300-400 degreeC environment.

  In this firing step, first, the surfactant contained in the porous carbon electrode substrate and the coating film is eliminated, and the water repellent particles are melted by heating the water repellent to near the melting point. By controlling the 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 base material >>
By the production method of the present invention, a porous carbon electrode for a polymer electrolyte fuel cell having a low electrical resistance and good drainage can be produced from a porous carbon electrode substrate. As long as it is a porous carbon electrode substrate, the above effect can be expressed by using the technique of the present invention rather than using 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 any conductive porous material such as conductive paper, cloth, non-woven fabric made of carbon powder, carbon fiber, metal fiber, and resin as conductive fillers. Specifically, commercially available carbon paper or the like can be used, but a porous carbon electrode base material in which short carbon fibers are bound by carbon can also be used. Examples of the carbon that binds the short carbon fibers include carbon fiber precursor short fibers, resins, and the like, and there is a method of carbonizing them by treating them at a high temperature. A carbon fiber sheet can be created from short carbon fibers and short fibers as a carbon source and a resin, and a porous carbon electrode base material in which carbon short fibers are bound by carbon can be manufactured through a molding and carbonization process. . These processes are desirably manufactured continuously from the viewpoint of quality and productivity. Moreover, not only said porous carbon electrode base material but the porous carbon electrode base material which does not have a carbonization process and has low energy cost can also be used. Examples of these materials include a porous carbon electrode base material in which fine conductive materials such as carbon fiber web and carbon are fixed with a binder such as a resin in which carbon short fibers are fixed with a binder filled with conductive material particles. and so on.

<Method for producing porous carbon electrode substrate>
In manufacturing a sheet-like material, a wet method in which a short carbon fiber (A) is dispersed in a liquid medium for paper making, a dry method in which the short carbon fiber (A) is dispersed in an air, and the like is deposited. The papermaking method can be applied. A wet method is preferred.

  By dispersing the carbon fiber precursor short fiber (b) and / or the fibrillar fiber (b ′) together with the carbon fiber (A), the carbon short fiber (A) and the carbon fiber precursor short fiber (b) and / or Alternatively, the strength of the sheet-like material is improved by entanglement with the fibrillar fibers (b ′), and the binder-free material can be made substantially free.

In the present invention, a small amount of an organic polymer compound may be used as a binder. The organic polymer compound used as the binder is not particularly limited, and examples thereof include polyvinyl alcohol (PVA) and polyester or polyolefin binders that are heat-sealed. The binder may be solid or liquid such as fibers or particles. The binder content 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 addition method of a binder is not specifically limited.

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

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

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

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

  When considering the spinnability and the short carbon fibers (A) from low temperature to high temperature, the remaining mass at the time of carbonization is large, and the fiber elasticity and fiber strength when performing the entanglement treatment described below, It is preferable to use an acrylic polymer containing 50% by mass or more of acrylonitrile units. Accordingly, the carbon fiber precursor fiber (b) is preferably an acrylic fiber or an acrylic fiber (containing 50% by mass or more of acrylonitrile units).

  One type of carbon fiber precursor short fiber (b) may be used, or two or more types of carbon fiber precursor short fibers (b) having different fiber diameters and polymer types may be used.

<Fibrous fiber (b ')>
As the fibrillar fiber (b ′), any fiber can be used regardless of whether it is a natural fiber or a synthetic fiber. For example, it includes fibrillar carbon precursor (b′-1) mainly composed of acrylic or the like to wood pulp which is a natural fiber. Among these, since it is preferable that the metal content is small, the fibrillar fiber (b ′) is preferably a synthetic fiber. More preferably, a fibrillar carbon precursor fiber (b′-1) or the like can be used. These may be used alone or in combination. Moreover, in order to improve a 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, easily splittable sea-island composite fiber cut to an appropriate length, and is fibrillated by beating with a refiner, a pulper, or the like. The fibrillar carbon precursor fiber (b′-1) is produced using two or more kinds of different polymers that are dissolved in a common solvent and are incompatible, and at least one kind of 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 fibers, those having a residual mass of 20% by mass or more in the carbonization treatment include acrylic polymers, cellulose polymers, and phenol polymers. Among them, it is preferable to use an acrylic polymer containing 50% by mass or more of an acrylonitrile unit from the viewpoint of spinnability and the remaining mass in the carbonization treatment step.

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

<Manufacture of paper bodies>
The following methods can also be used for the production of paper bodies. The short carbon fibers (A) cut to a suitable length are uniformly dispersed in water, the dispersed carbon short fibers are made on a net, and the made carbon short fiber sheet is immersed in an aqueous dispersion of polyvinyl alcohol. Then, the immersed sheet is pulled up and dried. The polyvinyl alcohol serves as a binder for binding the short carbon fibers, and in a state where the short carbon fibers are dispersed, a sheet of short carbon fibers in a state where they are bound by the binder is produced. In addition, styrene-butadiene rubber, epoxy resin, or the like can be used as the binder.

  As a method for producing a paper body in which short carbon fibers (A) and carbon fiber precursor fibers (b) and / or fibrillar fibers (b ′) are dispersed, short carbon fibers (A) in a liquid medium, Wet method in which carbon fiber precursor fibers (b) and / or fibrillar fibers (b ′) are dispersed to make paper, carbon short fibers (A) in the air, carbon fiber precursor fibers (b) and / or A paper making method such as a dry method in which the fibrillar fibers (b ′) are dispersed and accumulated can be applied. However, it is preferable to use a wet method from the viewpoint of high uniformity of the paper body.

  The mixing ratio of the carbon short fiber (A), the carbon fiber precursor fiber (b) and / or the fibrillar fiber (b ′) is 100 parts by weight of the carbon short fiber (A), and the carbon fiber precursor fiber ( It is preferable to mix so that the total amount of b) and a fibrillar fiber (b ') may be 20-100 weight part. When the total amount of the carbon fiber precursor fiber (b) and the fibrillar fiber (b ′) is small, the strength of the papermaking body is lowered, and the total amount of the carbon fiber precursor fiber (b) and the fibrillar fiber (b ′) is large. And the electrical conductivity of the porous carbon electrode base material obtained as a result will become low. The ratio of the carbon fiber precursor fiber (b) to 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 that it is contained in the ratio.

  Carbon fiber precursor fibers (b) and / or fibrillar fibers (b) are also used to help the short carbon fibers (A) open into single fibers and prevent the opened single fibers from refocusing. ´) is used. Further, if necessary, wet papermaking can be performed using a binder.

  A binder has a role as a glue which connects each component in the precursor sheet | seat containing a carbon short fiber (A) and a 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 power in the paper making process and the short carbon fibers (A) are less dropped. In the present invention, it is also possible to use the binder in a fiber shape.

  In the present invention, even if papermaking is performed without using a binder, an appropriate entanglement between the short carbon fiber (A) and the carbon fiber precursor fiber (b) and / or the fibrillar fiber (b ′) can be obtained. .

  Examples of the liquid medium in which the carbon short fibers (A) and the carbon fiber precursor fibers (b) and / or the fibrillar fibers (b ′) are dispersed include carbon precursor fibers (b) such as water and alcohol. Media that do not. Among these, it is preferable to use water from a viewpoint of productivity.

  It is preferable to use a medium such as water at a rate that the fiber concentration in the slurry in which the fiber is dispersed is about 1 to 50 g / L. If the fiber concentration in the slurry is low, the papermaking speed has to be slowed down, resulting in poor productivity, and if the fiber concentration is too high, the dispersibility of the fiber in the slurry is reduced. A lump is easily generated, and a papermaking body with large unevenness in weight per unit area is obtained.

  Examples of the method of mixing the short 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. From the viewpoint of uniformly dispersing, a method of diffusing and dispersing in water is preferable. The strength of the papermaking body is improved by mixing the short carbon fibers (A), the carbon fiber precursor fibers (b) and / or the fibrillar fibers (b ′), and making paper to produce a papermaking body. Can do. Moreover, it can prevent that the carbon short fiber (A) peels from a precursor sheet | seat during the manufacture, and the orientation of a carbon short fiber (A) changes.

Procedure (2) The process of performing the entanglement process on the paper body is not necessarily required, but the carbon short fiber (A) and the carbon fiber precursor short fiber (b) and / or by entanglement the sheet-like material A sheet (entangled structure sheet) having an entangled structure in which the fibrillar fibers (b ′) are entangled three-dimensionally can be formed.

  The entanglement process can be selected as needed from the method of forming the entangled structure, and is not particularly limited. A mechanical entanglement method such as a needle punching method, a high pressure liquid injection method such as a water jet punching method, a high pressure gas injection method such as a steam jet punching method, or a combination thereof can be used. It is possible to easily suppress the breakage of the short carbon fibers (A) and the breakage of the carbon fiber precursor short fibers (b) and / or the fibrillar fibers (b ′) in the entanglement treatment step, and appropriate entanglement The high-pressure liquid injection method is preferable in that the property 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 process of impregnating a papermaking body with a resin and drying / molding <Resin>
As the resin to be impregnated into the papermaking body, a known resin that can bind the carbon fiber of the gas diffusion layer at the stage of carbonization can be appropriately selected and used. When producing a porous carbon electrode substrate having a carbonization step, phenol resin, epoxy resin, furan resin, pitch, etc. are preferred from the viewpoint of easily remaining as a conductive substance after carbonization. In particular, a phenolic resin having a high carbonization rate is particularly preferred. When producing a porous carbon electrode base material that does not have a carbonization step, it can be used regardless of whether it is a thermoplastic or thermosetting resin. From the viewpoint of increasing the water repellency of the porous carbon electrode substrate, a fluororesin is preferred. It is also effective to mix carbon powder with these resins for the purpose of further improving the conductivity of the porous carbon electrode substrate regardless of the presence or absence of the carbonization step. Carbon powder includes graphite particles such as flaky graphite, flaky graphite, earthy graphite, artificial graphite, expanded graphite, expanded graphite, flake graphite, massive graphite, spherical graphite, carbon black, fullerene, carbon And nanotubes. Although not particularly limited, graphite particles and carbon black are more preferable among the 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. In particular, from the viewpoint of production cost, it is preferable to use a spray method or a curtain coat method.

<Drying and molding process>
A known technique can be used as a drying method. For example, a drum drying method in which a heated roll is brought into contact with the heated roll or a drying method using hot air can be used. From the standpoint of maintenance, drying by a non-contact method is preferable. The drying temperature is preferably 60 to 110 ° C., more preferably 70 to 100 ° C., at which the resin does not cure.

  The process of molding the paper body after resin impregnation and drying is important. When manufacturing the porous carbon electrode base material which has a carbonization process, the carbon short fiber (A) in a precursor sheet | seat is thereby made into carbon fiber precursor short fiber (b) and / or fibril-like carbon precursor fiber ( By fusing in b′-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 base material that does not have a carbonization process, the product dimensions are determined by the molding process, so the molten state of the fibrillated carbon precursor fiber (b′-1) and the resin is controlled. There must be. By performing heat treatment in an atmosphere of 200 to 400 ° C. after the molding, the manufacturing process of the carbonization step is completed.

  Any technique can be applied as long as the papermaking body can be uniformly heated and pressed. For example, a method in which a smooth rigid plate is applied to both sides of the paper body and hot-pressed, a continuous roll press apparatus, and a continuous belt press apparatus are used.

  In order to effectively smooth the surface of the precursor sheet, the heating temperature in the hot pressing is preferably less than 200 ° C, more preferably 120 to 190 ° C.

  Although the molding pressure is not particularly limited, when the content ratio of the carbon fiber precursor short fibers (b) and / or the fibrillar fibers (b ′) in the papermaking body is large, the sheet Y can be easily formed even if the molding pressure is low. The surface can be smoothed. If the press pressure is increased more than necessary at this time, there may be a problem that the short carbon fibers (A) are destroyed during the heat-pressure molding, a problem that the structure of the porous carbon electrode base material is too dense, or the like. There is. The molding pressure is preferably about 20 kPa to 10 MPa.

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

Procedure (4): The process of carbonizing the precursor sheet | seat obtained by the said procedure (3) at 2000-3000 degreeC in nitrogen atmosphere, and manufacturing a porous carbonaceous electrode base material .

<Carbonization>
The carbonization treatment carbonizes the carbon fiber precursor short fibers (b) and / or the fibrillar carbon precursor fibers (b ′) and the thermosetting resin in the precursor sheet. The carbonization treatment is preferably performed in an inert gas in order to increase the conductivity of the porous carbon electrode substrate. The carbonization treatment is usually performed at a temperature of 1000 ° C. or higher. The carbonization 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. Moreover, the pretreatment by baking in an inert atmosphere of about 300 to 800 ° C. can be performed before the carbonization treatment.

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

  A porous carbon electrode substrate can be obtained through the procedure described above. Procedure (2) and procedure (3) can be omitted.

<The manufacturing method of the porous carbon electrode base material which omitted the carbonization process>
By omitting the carbonization step, the energy cost can be greatly reduced as compared with the case of performing carbonization. In order to suppress a decrease in conductivity due to omission of the carbonization step, it is necessary to introduce a further conductive material. The above-described method for adding and fixing the conductive material to the paper body in which short carbon fibers are dispersed, and preparing a slurry comprising the conductive material and a binder resin, forming them, and then heat-treating them to make the porous body There is a method for producing a carbon electrode substrate. If it is the former method, according to the manufacturing method of the porous carbon electrode base material which has the carbonization process mentioned above, a conductive substance is added in the way of impregnating a paper body with resin, and it press-molds after that. The porous carbon electrode base material can be manufactured by fixing with the above. Also in the latter production method, in the same manner as the slurry preparation method in producing the paper body, a single or a plurality of conductive materials are selected, and a slurry is prepared by mixing in a solution with a binder material, A porous carbon electrode substrate can be produced by performing drying and heat treatment after film formation using a known coating technique. In addition, the conductive material to be used for these is not particularly limited. For example, in the case of carbon fiber, polyacrylonitrile-based (PAN-based) carbon fiber, pitch-based carbon fiber, rayon-based carbon fiber, others, carbon black, A carbon nanotube etc. can be used suitably. The kind to be used is not limited, and may be used alone or a plurality may be selected and used. As the binder for fixing the conductive substance, a resin can be used. As the resin, a fluorine-based or silicon-based resin having water repellency is preferable. In preparing the slurry, water, acetone, ethanol, methanol, or the like can be appropriately used as a solvent for the slurry, but water is used as the solvent from the viewpoint of reducing environmental burden and cost of manufacturing equipment. Is most preferred. Further, additives such as a surfactant and a sticking agent may be appropriately used to improve the dispersibility of the conductive substance and the binder substance in the slurry.

2. Porous carbon electrode The porous carbon electrode obtained by the production method of the present invention is a coating made of carbon powder and a water repellent on one surface of a porous carbon electrode base material in which short carbon fibers are bound by carbon. A porous carbon electrode in which a layer is formed, the electrical resistance in the direction perpendicular to the surface when a surface pressure of 0.5 MPa is applied is greater than 0.60 Ω · cm and less than or equal to 0.8 Ω · cm, and the following peeling It is a porous carbon electrode whose degree of exfoliation between the porous carbon electrode substrate and the coating layer obtained in the test is less than 50%.

<Peel test>
Tape: Nichiban Sealing Masking Tape No. 252
Size of test piece: 5 x 5 cm
Test Method: A tape cut to 3 × 3 cm is attached to the coating layer of the test piece, a load of 10 g / cm ² is applied to the adhesive surface for 30 seconds, and then the tape is peeled off. The area of the coating layer peeled off from the test piece and adhered to the tape is measured.

  Measure the area of the coating layer peeled off from the test piece and attached to the tape: The image of the tape surface to which the coating layer peeled off from the test piece was attached using a digital camera, the aspect ratio was 4: 3, and the number of recording pixels was 3648 × Shoot as 2736 pixels. Using the image analysis software Image-Pro Plus (manufactured by Nippon Roper) on the obtained image, the area of the coating layer having an area of 100 × 100 μm or more is measured, and the ratio to the tape area is calculated. The test is performed three times for one sample, and the degree of peeling is determined by the average value.

<Porous carbon electrode in which a coating layer made of carbon powder and a water repellent is formed on one surface of a porous carbon electrode substrate>
In the present invention, “the one in which a coating layer composed of carbon powder and a water repellent agent is formed on one surface of a porous carbon electrode substrate” is referred to as “porous carbon electrode”.

  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 Corporation), furnace black (for example, Vulcan XC72 manufactured by CABOT), etc. can be used. . The proportion of the carbon powder used is preferably such that the concentration when the carbon powder is dispersed in a solvent is 5 to 30%. Examples of the water repellent include fluororesins and silicon resins, which can be used by dispersing them in a solvent such as water. A fluororesin is particularly preferred 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. The ratio of the water repellent used is preferably such that the concentration when the water repellent is dispersed in the solvent is 5 to 60%.

  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 risk of organic solvents, cost, and environmental load, it is preferable to use water. When an organic solvent is used, it is preferable to use a lower alcohol, acetone or the like that is a solvent that can be mixed with water. As a ratio of using these organic solvents, it is preferable to use them at a ratio of 0.5 to 2 with respect to water 1.

  The coating layer composed of carbon powder and a water repellent is a combination of carbon powder and a water repellent that is a binder. In other words, carbon powder is taken into the network formed by the water repellent and has a fine network structure. When forming the coating layer, since a part of the composition penetrates into the porous carbon electrode substrate, it is difficult to define a clear boundary line between the coating layer and the porous carbon electrode substrate. The coating layer composition defines only the portion of the coating layer composition that does not penetrate into the porous carbon electrode substrate, that is, the layer composed only of carbon powder and a water repellent.

  The porous carbon electrode of the present invention has a coating layer made of carbon powder and a water repellent on either one of the surfaces of the porous carbon electrode substrate. The coating layer may be provided on both sides, but single-sided coating is preferable because productivity decreases due to an increase in the process, and gas diffusibility and drainage may be reduced by having a coating layer on both sides. . The surface on which the coating layer is formed may be either, but in order to form a strong coating layer, a surface having a certain degree of surface roughness is preferable. However, what formed the gas flow path in one surface of a porous carbon electrode base material is not this limitation, and it is preferable to form in the other smooth surface.

<Bulk density>
The bulk density of the porous carbon electrode of the present invention is preferably as high as possible from the viewpoint of lowering the electric resistance, but it is preferable that it is low from the viewpoint of the ability to discharge liquids and gases. Specifically, it is 0.30 to 0.65 g / cm ³ and is preferably in the range of 0.30 to 0.60 g / cm ³ .

  The bulk density of the present invention can be measured by a measurement method specifically described in the examples described later.

<Air permeability in the perpendicular direction>
The air permeability in the direction perpendicular to the plane of the porous carbon electrode of the present invention is 50 to 300 ml / hr · cm when measured by the Gurley method to be described later in order to keep the gas diffusibility good in addition to the liquid. ² mmAq. It is preferably 50 to 200 ml / hr · cm ² · mmAq.

The porous carbon electrode substrate used in the present invention preferably has an air permeability of 2000 to 20000 ml / hr · cm ² · mmAq in the direction perpendicular to the plane from the viewpoint of efficiently discharging the liquid.

<Thickness of porous carbon electrode>
The thickness of the porous carbon electrode is preferably in the range of 50 to 350 μm in order to develop good electrical conductivity and drainage. If it is 50 μm or more, handling is possible, and if it is 350 μm or less, good electrical conductivity is obtained. A more preferable thickness is in the range of 100 to 250 μm.

  <Electrical resistance in the direction perpendicular to the surface when 0.5 MPa is applied> The electrical resistance in the direction perpendicular to the surface of the porous carbon electrode of the present invention is 0.5 MPa. Since the balance with water repellency is important, the preferred range is 0.60 to 1.00 Ω · cm. More preferably, it is 0.60 to 0.80 Ω · cm.

  The “electrical resistance in the direction perpendicular to the surface when a surface pressure of 0.5 MPa is applied” of the present invention can be measured by a measurement method that will be described in detail in the examples described later.

<Adhesion rate of carbon powder and water repellent in porous carbon electrode substrate>
In the porous carbon electrode substrate of the porous carbon electrode of the present invention, the adhesion rate of the carbon powder and the water repellent decreases from the surface having the coating layer toward the surface not having the other coating layer. Yes.

  When forming the coating layer, the coating coating liquid soaks into the porous carbon electrode base material, thereby causing adhesion of carbon powder and water repellent. The adhesion rate can be controlled by the surface tension of the coating liquid and the formation time of the coating layer. In addition, the adhesion rate can be confirmed by observing the cross section of the porous carbon electrode with an electron microscope, and the pore structure derived from the porous carbon electrode substrate changes due to the change in the adhesion rate. I can do it. As described above, the method of the present invention can provide water repellency in the porous carbon electrode substrate when forming the coating layer. The process of impregnating the water repellent directly is not necessary. Further, according to the present invention, not only the process is reduced, but also the pore structure at the interface between the porous carbon electrode substrate and the coating layer is controlled, and the water repellency is stepped in the thickness direction in the porous carbon electrode substrate. Can be controlled.

Various physical property values were measured using the following methods.

<Calculation of bulk density>
From the produced porous carbon electrode, 10 3 × 3 cm square test pieces were randomly taken out, the thickness of each sample was measured with a micrometer at 5 points for each sample, and the average thickness was calculated. Weighed with a balance. The bulk density of the porous carbon electrode was calculated according to the following formula. The average value of the bulk density measured at 10 points was adopted as the representative value of the sample.

(Bulk density) = Test piece weight (g) / Test piece thickness (cm) / Test piece area (cm ² )
<Measurement of electric resistance in the direction perpendicular to the surface when a surface pressure of 0.5 MPa is applied>
The electrical resistance (through-direction resistance) in the thickness direction of the porous carbon electrode is obtained by sandwiching the porous carbon electrode between gold-plated copper plates, pressurizing at 0.5 MPa from the top and bottom of the copper plate, and applying a current at a current density of 10 mA / cm ^2. The resistance value when flowing was measured and calculated from the following equation. The sample size of the porous carbon electrode is diameter = 25 mm.

Through-direction resistance (mΩ · cm ² ) = Measured resistance value (mΩ) × Sample area (cm ² )
<Measurement of air permeability>
Based on JIS standard P-8117, the time required for 200 mL of air to permeate was measured using a Gurley densometer, and the gas permeability (ml / hr / cm ² / mmAq) was calculated.

<Peel test>
Tape: Nichiban Sealing Masking Tape No. 252
Size of test piece: 5 x 5 cm
Test Method: A tape cut to 3 × 3 cm is attached to the coating layer of the test piece, a load of 10 g / cm ² is applied to the adhesive surface for 30 seconds, and then the tape is peeled off. The area of the coating layer peeled off from the test piece and adhered to the tape is measured.

  Measure the area of the coating layer peeled off from the test piece and attached to the tape: An image of the tape surface to which the coating layer peeled off from the test piece was attached using a digital camera (manufactured by Panasonic, DMC-LX3) and an aspect ratio of 4 : 3, and the number of recorded pixels is 3648 × 2736 pixels. Using the image analysis software Image-Pro Plus (manufactured by Nippon Roper) on the obtained image, the area of the coating layer having an area of 100 × 100 μm or more is measured, and the ratio to the tape area is calculated. The test is performed three times for one sample, and the degree of peeling is determined by the average value.

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

  As the carbon short 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 carbon fiber precursor short fibers (b), acrylic short fibers (Mitsubishi Rayon Co., Ltd., trade name: D122) having an average fiber diameter of 4 μm and an average fiber length of 3 mm, and fibrillar fibers (b ′) , An easily split fiber acrylic sea-island composite short fiber (made by Mitsubishi Rayon Co., Ltd., trade name: Bonnell MVP-C651, made of an acrylic polymer fibrillated by beating and diacetate (cellulose acetate), Average fiber length: 3 mm) was prepared.

  A porous carbon electrode was produced by the following operations <1> to <10>.

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

<2> Disaggregation of carbon fiber precursor short fibers (b) The carbon fiber precursor short fibers (b) are dispersed in water so that the fiber concentration is 1% (10 g / L), and then disaggregated through a mixer. A disaggregated slurry fiber (Sb) was obtained.

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

<4> Manufacture of papermaking body The carbon short fiber (A), the carbon fiber precursor short fiber (b), and the fibrillar fiber (b ′) are in a mass ratio of 70:10:20, and the concentration of fibers in the slurry. However, the disaggregation slurry fiber (SA), the disaggregation slurry fiber (Sb), the disaggregation slurry fiber (Sb ′), and the dilution water were weighed and dispersed so as to be 1.44 g / L. For papermaking, a sheet drive unit consisting of a net drive unit and a flat net mesh made of plastic net with a width of 60cm x length of 585cm connected in a belt shape and continuously rotated, the slurry supply unit width is 48cm, the bottom of the net A processing apparatus consisting of a vacuum dehydration apparatus arranged in the above was used. A pressurized water jet treatment apparatus provided with the following three water jet nozzles was disposed downstream of the treatment apparatus.

Nozzle 1: hole diameter φ0.15mm × 501 hole
Width direction hole pitch 1mm (1001 hole / width 1m)
1 row arrangement, nozzle effective width 500mm
Nozzle 2: hole diameter φ0.15 mm × 501 hole
Width direction hole pitch 1mm (1001 hole / width 1m)
1 row arrangement, nozzle effective width 500mm
Nozzle 3: hole diameter φ0.15 mm × 1002 holes
Width direction hole pitch 1.5mm
3 rows, 5 mm pitch between rows, 500 mm nozzle effective width
The pressurized water jet pressure is 1MPa nozzle 1, pressure 2MPa (nozzle 2), pressure 1MPa (nozzle 3), and the slurry in which the fibers are dispersed is introduced from the slurry supply unit, and after dehydration under reduced pressure, nozzle 1, nozzle 2, nozzle The papermaking body having a three-dimensional entanglement structure was obtained by passing through in the order of 3 and applying entanglement treatment. The paper body was dried at 150 ° C. for 3 minutes using a pin tenter tester (PT-2A-400 manufactured by Sakurai Dyeing Machine Co., Ltd.) to obtain a paper body. In addition, the dispersion state of the carbon short fiber (A), the carbon fiber precursor short fiber (b), and the fibrillar fiber (b ′) in the papermaking body was good, and the handling property was also good.

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

<6> Pressurization and heating molding Next, both sides of this papermaking body are arranged so as to be sandwiched by paper coated with a silicone release agent, and at 190 ° C. and a belt speed of 0.2 m / min with a double belt press device. The press molding was performed.

<7> Carbonization treatment Thereafter, the precursor sheet was carbonized in a batch carbonization furnace in a nitrogen gas atmosphere at 2000 ° C. for 1 hour to obtain a porous carbon electrode substrate. The obtained porous carbon electrode substrate was smooth without warping or undulation.
<8> Preparation of Coating Solution 1 Denka Black (manufactured by Denki Kagaku Kogyo Co., Ltd.), ion-exchanged water, and isopropyl alcohol are mixed at a ratio of 5: 100: 80, respectively, and a homomixer MARK-II (manufactured by Primix Co., Ltd.) is 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 After cooling the coating liquid 1 and setting the liquid temperature to 10 ° C. or lower, the polytetrafluoroethylene (PTFE) dispersion is cooled at a ratio of 0.3 to the carbon black 1 while cooling. The mixture was added and stirred at 500 rpm for 5 minutes with a disper to obtain coating liquid 2.

<10> Preparation of water-repellent treatment liquid for porous carbon electrode substrate PTFE dispersion (31-JR, manufactured by Mitsui DuPont Fluorochemical) and interface are used for preparation of water-repellent treatment liquid for porous carbon electrode substrate. An activator (polyoxyethylene (10) octylphenyl ether) and distilled water were used. After adjusting the solid content concentration in the water-repellent treatment liquid to 1 wt% for PTFE and 2 wt% for the surfactant, water was added by adding distilled water and stirring at 1000 rpm for 10 minutes using a disper. A treatment solution was prepared.

<11> Impregnation of porous carbon electrode base material with water-repellent treatment liquid The porous carbon electrode base material was impregnated by being immersed in the water-repellent treatment liquid. The impregnated porous carbon electrode substrate is allowed to stand on the glass surface of an applicator (manufactured by Tester Sangyo), the attached applicator bar is pressed against the porous carbon electrode substrate, and the applicator bar is conveyed at a speed of 100 mm / sec. As a result, excess water-repellent treatment liquid adhering to the porous carbon electrode substrate was removed.

<12> Formation of coating layer Furthermore, the coating liquid 2 was coated on the porous carbon electrode substrate using an applicator (manufactured by Tester Sangyo), and then dried for 20 minutes using a hot air dryer set at 100 ° C. It was. Further, after drying, a porous carbon electrode was obtained by performing a sintering process at 360 ° C. for 1 hour in a muffle furnace to form a coating layer. The obtained porous carbon electrode had good bulk density of 0.30 g / cm ³ , penetration resistance of 0.611 Ω · cm, and air permeability of 122.2 ml / hr · cm ² · mmAq. Moreover, when the obtained porous carbon electrode was used for the peeling test and the peeling degree was computed, it was as low as 5.2%, and the adhesiveness of a coating layer and a porous carbon electrode base material was favorable. Table 1 summarizes the results.
<Example 2>
A porous carbon electrode was obtained in the same manner as in Example 1 except that the concentration of PTFE in the water-repellent treatment liquid for the porous carbon electrode substrate was 5 wt%. The obtained porous carbon electrode had good bulk density of 0.43 g / cm ³ , penetration resistance of 0.622 Ω · cm, and air permeability of 93.0 ml / hr · cm ² · mmAq. Moreover, when the obtained porous carbon electrode was used for the peeling test and the peeling degree was computed, it was as low as 12.5% and the adhesiveness of a coating layer and a porous carbon electrode base material was favorable. Table 1 summarizes the results.

<Example 3>
A porous carbon electrode was obtained in the same manner as in Example 1 except that the concentration of PTFE in the water-repellent treatment liquid for the porous carbon electrode substrate was 10 wt%. The obtained porous carbon electrode had good bulk density of 0.37 g / cm ³ , penetration resistance of 0.632 Ω · cm, and air permeability of 106.0 ml / hr · cm ² · mmAq. Moreover, when the obtained porous carbon electrode was used for the peeling test and the peeling degree was calculated, it was as low as 40.2% and the adhesiveness of a coating layer and a porous carbon electrode base material was favorable.
<Example 4>
A porous carbon electrode was obtained in the same manner as in Example 1 except that the concentration of PTFE in the water-repellent treatment liquid for the porous carbon electrode substrate was 20 wt%. The obtained porous carbon electrode had good bulk density of 0.37 g / cm ³ , penetration resistance of 0.632 Ω · cm, and air permeability of 106.0 ml / hr · cm ² · mmAq. Moreover, when the obtained porous carbon electrode was used for the peeling test and the peeling degree was calculated, it was as low as 40.2% and the adhesiveness of a coating layer and a porous carbon electrode base material was favorable.
<Example 5>
A porous carbon electrode was obtained in the same manner as in Example 1 except that the concentration of PTFE in the water-repellent treatment liquid for the porous carbon electrode substrate was 30 wt%. The obtained porous carbon electrode had good bulk density of 0.37 g / cm ³ , penetration resistance of 0.632 Ω · cm, and air permeability of 106.0 ml / hr · cm ² · mmAq. Moreover, when the obtained porous carbon electrode was used for the peeling test and the peeling degree was calculated, it was as low as 40.2% and the adhesiveness of a coating layer and a porous carbon electrode base material was favorable.

<Comparative Example 1>
Example 1 except that the porous carbon electrode base material was impregnated with a water-repellent treatment solution, then treated with a hot air dryer at 100 ° C. for 20 minutes and completely dried to form a coating layer. In the same manner, a porous carbon electrode was obtained. The obtained porous carbon electrode had good bulk density of 0.33 g / cm ³ , penetration resistance of 0.679 Ω · cm, and air permeability of 48.0 ml / hr · cm ² · mmAq. However, when the obtained porous carbon electrode was subjected to a peeling test and the degree of peeling was calculated, it was as large as 62.1%, and the adhesion between the coating layer and the porous carbon electrode substrate was poor.
<Comparative example 2>
Example 2 except that the porous carbon electrode base material was impregnated with a water repellent treatment solution, then treated with a hot air dryer at 100 ° C. for 20 minutes and completely dried to form a coating layer. In the same manner, a porous carbon electrode was obtained. The obtained porous carbon electrode had good bulk density of 0.46 g / cm ³ , penetration resistance of 0.666 Ω · cm, and air permeability of 50.1 ml / hr · cm ² · mmAq. However, when the obtained porous carbon electrode was subjected to a peeling test and the degree of peeling was calculated, it was as large as 65.3%, and the adhesion between the coating layer and the porous carbon electrode substrate was poor.

<Comparative Example 3>
Example 3 except that the porous carbon electrode base material was impregnated with a water repellent treatment solution, then treated with a hot air dryer at 100 ° C. for 20 minutes and completely dried to form a coating layer. In the same manner, a porous carbon electrode was obtained. The obtained porous carbon electrode had good bulk density of 0.38 g / cm ³ , penetration resistance of 0.689 Ω · cm, and air permeability of 30.3 ml / hr · cm ² · mmAq. However, when the obtained porous carbon electrode was subjected to a peeling test and the degree of peeling was calculated, it was as large as 70.3%, and the adhesion between the coating layer and the porous carbon electrode substrate was poor.
<Comparative Example 4>
A porous carbon electrode was obtained in the same manner as in Example 1 except that the concentration of PTFE in the water-repellent treatment liquid for the porous carbon electrode substrate was 20 wt%. The obtained porous carbon electrode had good bulk density of 0.37 g / cm ³ , penetration resistance of 0.632 Ω · cm, and air permeability of 106.0 ml / hr · cm ² · mmAq. However, when the obtained porous carbon electrode was subjected to a peeling test and the degree of peeling was calculated, it was as large as 70.3%, and the adhesion between the coating layer and the porous carbon electrode substrate was poor.
<Comparative Example 5>
A porous carbon electrode was obtained in the same manner as in Example 1 except that the concentration of PTFE in the water-repellent treatment liquid for the porous carbon electrode substrate was 30 wt%. The obtained porous carbon electrode had good bulk density of 0.37 g / cm ³ , penetration resistance of 0.632 Ω · cm, and air permeability of 106.0 ml / hr · cm ² · mmAq. However, when the obtained porous carbon electrode was subjected to a peeling test and the degree of peeling was calculated, it was as large as 77.6%, and the adhesion between the coating layer and the porous carbon electrode substrate was poor.

Claims (5)

A method for producing a porous carbon electrode, comprising the following steps [1] to [4].
Step [1]: A step of impregnating a porous carbon electrode base material in which short carbon fibers are bound with carbon with a solution containing a water repellent and a surfactant.
Step [2]: A coating solution composed of carbon powder and a water repellent agent is applied onto a porous carbon electrode substrate impregnated with a solution containing a water repellent agent and a surfactant to form a uniform coating film. Process.
Step [3]: A step of drying the porous carbon electrode substrate on which the coating film is formed in an environment of 50 to 200 ° C.
Step [4]: A step of producing a porous carbon electrode by firing the porous carbon electrode substrate on which the dried coating film has been formed in an environment of 300 to 400 ° C.   The production method according to claim 1, wherein the surfactant is polyoxyethylene (10) octylphenyl ether, and the concentration is 0.1 to 5 wt% or less.   The porous carbon electrode manufactured by the method of Claim 1 or 2. A porous carbon electrode in which a coating layer composed of carbon powder and a water repellent is formed on one surface of a porous carbon electrode base material in which short carbon fibers are bound by carbon, and the surface pressure is 0.5 MPa. The degree of peel between the porous carbon electrode substrate and the coating layer obtained by the following peel test is such that the electrical resistance in the direction perpendicular to the surface when applied is 0.60 Ω · cm and 0.8 Ω · cm or less. A porous carbon electrode that is less than 50%.
<Peel test>
Tape: Nichiban Sealing Masking Tape No. 252
Size of test piece: 5 x 5 cm
Test Method: A tape cut to 3 × 3 cm is attached to the coating layer of the test piece, a load of 10 g / cm ² is applied to the adhesive surface for 30 seconds, and then the tape is peeled off. The area of the coating layer peeled off from the test piece and adhered to the tape is measured.
Measure the area of the coating layer peeled off from the test piece and attached to the tape: The image of the tape surface to which the coating layer peeled off from the test piece was attached using a digital camera, the aspect ratio was 4: 3, and the number of recording pixels was 3648 × Shoot as 2736 pixels. Using the image analysis software Image-Pro Plus (manufactured by Nippon Roper) on the obtained image, the area of the coating layer having an area of 100 × 100 μm or more is measured, and the ratio to the tape area is calculated. The test is performed three times for one sample, and the degree of peeling is determined by the average value.   The porous carbon electrode according to claim 4, wherein a coating layer composed of carbon powder and a water repellent is formed on the rough surface of the porous carbon electrode substrate.