JP2022082646A - Porous electrode base material, gas diffusion layer, gas diffusion electrode, and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous electrode base material from which an excess binder at a carbon fiber binding portion on the surface of the base material is sufficiently removed, and which are less likely to cause a short circuit or cross leakage of reaction gas when used in a fuel cell, a gas diffusion layer, and a gas diffusion electrode.

SOLUTION: There is provided a carbon fiber sheet to which the carbon fibers are bound, a porous electrode base material for a polymer electrolyte fuel cell in which the maximum thickness of a binder attached to a carbon fiber binding portion on the surface of the sheet is within 5 μm, and a gas diffusion layer for a polymer electrolyte fuel cell, preferably formed by forming a coating layer composed of carbon powder and a water repellent on at least one surface of the porous electrode base material for the polymer electrolyte fuel cell.

SELECTED DRAWING: None

COPYRIGHT: (C)2022,JPO&INPIT

Description

The present invention relates to a porous electrode base material, a gas diffusion layer, a gas diffusion electrode, and a method for producing the same.

A base material using carbon fibers such as carbon fiber paper, carbon fiber cloth, and carbon fiber felt is generally used for the gas diffusion layer of the solid polymer fuel cell and the electrode of the redox flow battery. Not only do these substrates exhibit high conductivity due to carbon fiber, but because they are porous materials, they are highly permeable to fuel gas and liquids such as generated water and electrolytic solutions, making them suitable materials for gas diffusion layers. ..

However, the gas diffusion layer of the polymer electrolyte fuel cell and the base material used as the electrode of the redox flow battery are carbon due to friction and compression generated in the bonding process of the electrolyte membrane and the fastening process of the stack when manufacturing the battery. There is a risk of fiber fluffing, falling off, or breaking. Since these carbon fibers and resin carbides that have fallen off or broken are more rigid than the electrolyte membrane, they may pierce the electrolyte membrane.

By piercing the electrolyte film, a short circuit occurs between the anode electrode and the cathode electrode, and a problem such as cross-leakage of the electrolyte and / or the hydrogen gas on the anode electrode side and / or the oxygen gas on the cathode electrode side occurs. The electrolysis and durability of the fuel cell and the redox flow battery tended to be significantly impaired.

By the way, as a method for reducing damage caused by piercing the carbon fiber into the electrolyte membrane, for example, Patent Document 1 describes in advance the surface pressure applied to the gas diffusion layer in the bonding step with the electrolyte membrane and the catalyst layer and the stack fastening step. Disclosed is a method of preliminarily removing the weakly bound carbon fiber and the carbon fiber that has fallen off or is damaged. Further, Patent Document 2 discloses a method of removing fluff on the surface of the carbon paper by press-fitting the carbon paper between a pair of elastic rolls.

Japanese Unexamined Patent Publication No. 2009-190951 Japanese Unexamined Patent Publication No. 2016-143468

However, although the carbon powder generated in the subsequent step by pressing can be removed in advance by the method described in Patent Document 1, the generated carbon powder is insufficient because the pressure applied at the time of pressing and the removal treatment after pressing are insufficient. Was not sufficiently removed, and there was a risk that a short-circuit current would occur when used in a fuel cell.

The method described in Patent Document 2 has a problem that the deformation amount in the thickness direction of the carbon paper cannot follow the deformation amount of the elastic roll, and the carbon paper is liable to break during continuous operation.
The present invention overcomes the above-mentioned problems and is less likely to cause a short circuit, a reaction gas, or a cross leak of an electrolytic solution when used in a fuel cell or a redox flow battery. It is an object of the present invention to provide a porous electrode base material from which excess binder in a bonded portion is sufficiently removed, a gas diffusion layer, a gas diffusion electrode, and a method for producing the same.

As a result of diligent studies to solve the above problems, the present inventors have completed the present invention. That is, the gist of the present invention lies in the following (1) to (7).
(1) A carbon fiber sheet in which carbon fibers are bound by carbon, and a porous electrode base material having a maximum thickness of a binder attached to a carbon fiber bound portion on the sheet surface of 5 μm or less.
(2) The thickness of the porous electrode substrate according to (1) above is 80 to 300 μm, the bulk density is 0.18 to 0.42 g / cm ³ , and the penetration resistance is 3.0 to 7.0 mΩ · cm. ^2. Solid polymer type having an air permeability in the thickness direction of 0.2 to 7.1 L / (m ² · Pa · s) and having a coating layer composed of carbon powder and a water repellent on at least one surface. Gas diffusion layer for fuel cells.
(3) A polymer electrolyte gas diffusion electrode having an electrode catalyst layer on a coating layer of the gas diffusion layer for a polymer electrolyte fuel cell according to (2) above.
(4) The porous electrode base material according to (1) above, the gas diffusion layer for a polymer electrolyte fuel cell according to (2) above, or the polymer electrolyte gas diffusion electrode according to (3) above. Membrane electrode assembly for polymer electrolyte fuel cell used.
(5) The method for producing a gas diffusion layer for a polymer electrolyte fuel cell according to (2) above, which comprises the following steps [1] to [6].
Step [1]: The porous electrode base material is held by a roll having a diameter of 40 to 150 mm at an angle of 2 to 180 ° along the sheet flow direction, and is run at a sheet tension of 10 to 100 N / m to be porous. A process of desorbing weakly bonded carbon powder contained in the electrode base material.
Step [2]: The carbon powder on the porous electrode base material obtained in the above step [1] and the excess binder of the carbon fiber binding portion are continuously removed by a rotary brush having a wire diameter of 0.05 mm to 0.3 mm. The process of squeezing.
Step [3]: A step of removing the carbon powder on the porous electrode base material obtained in the above step [2].
Step [4]: A step of forming a coating layer by applying a coating liquid consisting of a conductive agent, a water repellent agent, a surfactant, and water on the porous electrode base material obtained in the above step [3].
Step [5]: A step of heating the coating layer formed on the porous electrode substrate in the above step [4] to 50 to 150 ° C. and drying the coating layer.
Step [6]: A step of heating the porous electrode base material on which the coating layer is formed in the above step [5] to 200 to 400 ° C. and sintering the water repellent to obtain a gas diffusion layer.

(6) The method for producing a gas diffusion layer for a polymer electrolyte fuel cell according to (5) above, which comprises the following step [1'] instead of the step [1].
Step [1']: The porous electrode base material is pressed with a rubber roll having a JIS-A rubber hardness of A60 to A100 and a metal roll plated with hard chrome with a load of 1 to 10 kN to obtain the porous electrode. A process of removing weakly bonded carbon powder contained in a base material.

(7) The method for producing a polymer electrolyte gas diffusion electrode according to (3) above, which comprises the following step [7] after the steps [6] of (5) and (6).
Step [7]: A step of forming an electrode catalyst layer on the gas diffusion layer on which the coating layer is formed.

Porous electrode base material from which excess binder at the carbon fiber binding portion on the surface of the base material is sufficiently removed, which is less likely to cause short circuit or cross leakage of reaction gas and electrolyte when used in fuel cells and redox flow batteries. , A gas diffusion layer, and a gas diffusion electrode can be obtained.

Hereinafter, the present invention will be described in detail.
The porous electrode base material, the gas diffusion layer, and the gas diffusion electrode of the present invention can be manufactured, for example, by the following steps (1) to (6).
(1) A step of manufacturing a porous electrode base material in which carbon fibers are bound by carbon or the like.
(2) The gas diffusion layer is formed by holding the porous electrode base material on a roll having a diameter of 40 to 150 mm at an angle of 2 to 180 ° along the sheet flow direction and running it with a sheet tension of 10 to 100 N / m. A step of removing weakly bonded carbon powder contained in a base material.
(3) The porous electrode base material is pressed into the porous electrode base material with a rubber roll having a JIS-A rubber hardness of A60 to A100 and a metal roll plated with hard chrome with a load of 1 to 10 kN. Step of removing the carbon powder having a weak bond contained in (4) Next, a step of continuously removing the carbon powder adhering to the porous electrode base material.
(5) A step of obtaining a gas diffusion layer in which a coating layer is formed on the porous electrode base material obtained in (4) above.
(6) A step of forming an electrode catalyst layer on the coating layer of the gas diffusion layer obtained in (5) above to obtain a gas diffusion electrode.

<(1) Step of manufacturing a porous electrode base material in which carbon fibers are bound by carbon or the like>
First, in the first step, a porous electrode base material in which carbon fibers are bound by carbon or the like is manufactured. Here, the porous electrode base material is, for example, a paper making step of making carbon fibers to obtain carbon fiber paper, a resin impregnation step of impregnating the carbon fiber paper with a resin, and heating the carbon fiber paper impregnated with the resin. It is manufactured by undergoing a carbonization step of carbonizing the resin. The porous electrode base material to be produced is preferably a papermaking body formed by aggregating a plurality of carbon fibers having high surface smoothness, good electrical contact, and high mechanical strength. By selecting a conductive component as a binder for fixing carbon fibers to each other, it is possible to omit the above carbonization step and manufacture a porous electrode base material at low cost.

The carbon fiber can be used regardless of its raw material, but one or more selected from polyacrylonitrile (hereinafter abbreviated as PAN) -based carbon fiber, pitch-based carbon fiber, rayon-based carbon fiber, and phenol-based carbon fiber. It preferably contains carbon fibers, and more preferably contains PAN-based carbon fibers or pitch-based carbon fibers.

The average diameter of the carbon fibers is preferably about 3 to 30 μm, more preferably 4 to 20 μm, still more preferably 4 to 14 μm. Within this range, the surface smoothness and conductivity of the porous electrode base material are good.
The average length of the carbon fibers is preferably 2 to 16 mm, more preferably 3 to 9 mm. Within this range, the dispersibility during papermaking and the mechanical strength as a porous electrode base material become high.

As the carbon material for binding the carbon fibers to each other, a carbon material obtained by carbonizing a resin by heating can be used. As the resin used for this purpose, a known resin capable of binding the carbon fibers of the porous electrode base material at the stage of carbonization can be appropriately selected and used. From the viewpoint that it easily remains as a conductive substance after carbonization, phenol resin, epoxy resin, furan resin, pitch and the like are preferable, and phenol resin having a high carbonization rate at the time of carbonization by heating is particularly preferable. In the case of not undergoing carbonization, by adding graphite, carbon black, carbon nanotubes, etc. in addition to polytetrafluoroethylene that can guarantee water repellency in addition to the above resin, a porous electrode with high conductivity without undergoing carbonization is added. A base material can be obtained.

The carbonization of the carbon material can be carried out by firing at 1500 to 2200 ° C. in an inert gas.
By performing thermoforming and oxidation treatment before carbonization, it is possible to produce a porous electrode base material having a higher residual carbon content, higher surface smoothness, and less thickness variation.

The thickness of the porous electrode base material is usually preferably 50 to 500 μm, more preferably 50 to 300 μm. If it is within this range, it can be easily wound into a roll and can maintain high sheet strength.
In the second step, the porous electrode base material obtained as described above is held by a roll having a diameter of 40 to 150 mm at an angle of 2 to 180 ° along the sheet flow direction to a sheet tension of 10 to 100 N / m. The carbon powder with a weak bond contained in the porous electrode base material is desorbed by running the powder.

<(2) The porous electrode base material is held in a roll having a diameter of 40 to 150 mm at an angle of 2 to 180 ° along the sheet flow direction, and is run at a sheet tension of 10 to 100 N / m to be porous. Step to remove carbon powder with weak bond contained in the electrode base material>

The porous electrode base material is usually pressurized when it is adhered to a polymer electrolyte membrane or a catalyst layer, or when it is incorporated into a battery. At this time, the carbon fiber pieces and carbon powder adhering to the surface of the porous electrode base material cause damage to the polyelectrolyte film. Therefore, by going through the second step, the carbon fibers and carbon powder that fall off from the porous electrode base material due to pressurization can be removed in advance, and the damage to the polyelectrolyte film can be reduced.
By arranging such a porous electrode base material according to the present invention in a membrane-electrode assembly or a polymer electrolyte fuel cell, a solid polymer fuel cell or a redox can be used when assembling the membrane-electrode assembly. It is possible to reduce the damage caused by the carbon fiber and the carbon powder to the polymer electrolyte membrane during the production of the flow battery cell or the pressurization during power generation.

Here, the "sheet flow direction" refers to the direction in which the porous electrode base material is conveyed. A roll having a diameter of 40 to 150 mm is suitable for holding the porous electrode base material. If the diameter is 40 mm or more, the porous electrode base material can be stably transported without cracking, and if it is 150 mm or less, the carbon fibers and carbon powder adhering to the porous electrode base material are sufficiently desorbed. It is possible. The surface texture of the roll may be any material as long as it does not damage the surface of the porous electrode base material, and rubber, various metals, carbon and the like can be used. From the viewpoint of not easily contaminating the roll, it is preferable to use a roll plated with hard chrome. The angle at which the porous electrode base material is held is preferably 2 to 180 degrees with respect to the center of the roll. If the angle is small, it becomes difficult to separate the carbon fiber and carbon powder by hugging them.

<(3) The porous electrode base material is pressed with a rubber roll having a JIS-A rubber hardness of A60 to A100 and a metal roll plated with hard chrome with a load of 1 to 10 kN. Step to remove carbon powder with weak bond contained in>
By step 3 instead of step 2, the porous electrode base material can be pressed to desorb the carbon powder having a weak bond contained in the porous electrode base material. A pair of rolls is used for the press, one is a rubber roll and the other is a metal roll. As the hardness of the rubber roll, the rubber hardnesses A60 to A100 specified by JIS K6523 are preferable. By setting the rubber hardness within the above range, it is possible not only to break the raised carbon fibers but also to break the weak portion in the carbon fiber binding portion in the porous electrode base material. Further, since it is possible to follow the deformation of the porous electrode base material, it is possible to perform stable processing without causing cracks or the like. By using a metal roll plated with hard chrome for the other roll, it is more rigid than the porous electrode base material, so that it can be uniformly pressed with a predetermined load. As the load applied at the time of pressing, a load of 1 to 10 kN is preferable, and if it is 1 kN or more, it is sufficient to break the raised carbon fibers, and it is possible to break the weakly bound portion. If it is less than 10 kN, it can be uniformly treated without destroying the main part of the porous electrode base material.

<(4) Next, a step of continuously removing carbon powder adhering to the porous electrode base material>
In step 4, carbon powder containing carbon fibers generated in the upstream step is removed. Non-contact method, contact method, or both can be applied to the removal. The non-contact method has the advantage that it does not damage the porous electrode base material, but it cannot be removed because it is difficult to wind up the small carbon powder with air. Contact-type cleaning is effective for small-sized carbon powder. A rotating brush can be applied as the contact method. The material of the brush used for the rotating brush may be any material that does not damage the porous electrode base material, and various plastics such as nylon, polypropylene, and conductive fibers are used to prevent the brush and the porous electrode base material from being contaminated by charging. It is preferable to use the part.

The fiber diameter of the brush is preferably 0.02 mm to 0.5 mm, preferably 0.05 to 0.3 mm, from the viewpoint of invading the pores of the porous electrode base material and removing the excess binder at the carbon fiber binding portion. Is even more preferable. If the fiber diameter is made too small, the brush will lose its waist and the scraping force will be reduced. On the other hand, if the fiber diameter is made too large, the brush is stiff and the surface of the gas diffusion layer is scraped off more than necessary, which is not preferable. Also, when using a brush with a small fiber diameter, the brushes tend to get entangled with each other, so by putting a crimp in the fiber, the fibers should not be entangled with each other and the brush tips should be treated so that they are independent. Is preferable. The number of rotations of the rotating brush can be changed according to the line speed. A preferred range is 60 to 1200 rpm, and a more preferred range is 60 to 400 rpm. By rotating the porous electrode base material in both the forward direction and the reverse direction with respect to the flow of the porous electrode base material, it is possible to uniformly remove the carbon fiber fragments randomly arranged on the plane. The pushing amount of the rotating brush is preferably 0.2 to 5.0 mm based on the position where the porous electrode base material and the tip of the brush come into contact with each other.

<(5) A step of obtaining a gas diffusion layer in which a coating layer is formed on the porous electrode base material obtained in (4). ＞
In step 5, a coating layer is formed on the porous electrode base material obtained up to step 4, and a gas diffusion layer is obtained. The "coating layer" referred to here refers to a layer composed of a conductive agent and a water repellent agent, which is arranged on at least one surface of the porous electrode base material. As the conductive agent used for the coating layer, carbon powder or the like can be used. As the carbon powder, for example, graphite powder, carbon black, carbon nanotubes, carbon nanofibers and the like can be used. Above all, it is preferable to use carbon black from the viewpoint of manufacturing cost. For example, furnace black (for example, Balkan XC72 manufactured by CABOT), acetylene black (for example, Denka black manufactured by Electrochemical Industry Co., Ltd.), Ketjen black (for example, Ketjen Black EC manufactured by Lion Co., Ltd.) and the like can be used. .. As the ratio of using the carbon powder, it is preferable to use it so that the concentration when the carbon powder is dispersed in the solvent is 5 to 30%. Examples of the water repellent agent include fluororesin and silicone resin, and these can be dispersed in a solvent such as water and used. Fluororesin is particularly preferable because of its high water repellency. Examples of the fluororesin include tetrafluoroethylene-hexafluoropropylene copolymer, polytetrafluoroethylene (PTFE), tetrafluoroethylene-ethylene copolymer and the like, and PTFE is particularly preferable. As a ratio of using the water repellent agent, it is preferable to use the water repellent agent so that the concentration when the water repellent agent is dispersed in the solvent is 5 to 60%. In the present invention, in order to make the water repellent into fibers, PTFE produced by emulsion polymerization is preferable, and the dispersion type is particularly preferable.

Water or an organic solvent can be used as the solvent for dispersing the carbon powder and the water repellent. It is preferable to use water from the viewpoint of the danger, cost and environmental load of the organic solvent. However, since carbon powder is highly hydrophobic and does not disperse in water as it is, it can be dispersed in water by using a surfactant or the like. When using an organic solvent, it is preferable to use a lower alcohol or acetone which is a solvent that can be mixed with water. The ratio of these organic solvents to water 10 is preferably 0.5 to 2.

The coating layer composed of the carbon powder and the water repellent is formed by binding the carbon powder with the water repellent which is a binder. In other words, carbon powder is incorporated into the network formed by the water repellent agent and has a fine network structure. It is difficult to define a clear boundary line between the coating layer and the porous electrode base material because a part of the composition soaks into the porous electrode base material when the coating layer is formed. Only the portion where the coating layer composition does not soak into the porous electrode base material, that is, the layer composed of carbon powder and the water repellent agent, is defined as the coating layer. Shape The gas diffusion layer of the present invention has a coating layer composed of carbon powder and a water repellent on either one of the surfaces of the porous electrode base material. Although the coating layer may be provided on both sides, single-sided coating is preferable because the increase in the process may reduce productivity and the presence of the coating layer on both sides may reduce gas diffusivity and drainage. .. The surface on which the coating layer is formed may be either, but in order to form a strong coating layer, it is preferable that the surface has a certain degree of surface roughness. However, the case where the gas flow path is formed on one surface of the porous electrode base material is not limited to this, and it is preferable to form the gas flow path on the other smooth surface.

<Steps of forming an electrode catalyst layer on the coating layer of the gas diffusion layer obtained in (6) and (5) to obtain a gas diffusion electrode>
The electrode catalyst layer referred to here is a layer composed of platinum-supported carbon as a catalyst and a polymer having an ion exchange ability as a binder, and is a reaction field in which an oxidation reaction of hydrogen and a reduction reaction of oxygen occur. Platinum is not used as the catalyst. For example, another metal or a carbon alloy catalyst may be applied. Further, as the binder, not only a fluorine-based ion exchange resin but also a hydrocarbon-based ion exchange resin can be applied. Efficient power generation can be achieved by setting the thickness of the catalyst layer to 2 to 30 μm. As a method for forming the catalyst layer, various coating methods can be applied. Examples thereof include a bar coating method, a blade method, a screen printing method, a spray method, a curtain coating method and a roll coating method. By these methods, a uniform catalyst layer film can be formed on the coating layer of the gas diffusion layer. The coated film of the formed catalyst layer is dried by a general method to produce a gas diffusion electrode having the catalyst layer formed.
The porous electrode base material of the present invention is a carbon fiber sheet in which carbon fibers are bound by carbon, and the maximum thickness of the binder attached to the carbon fiber bound portion on the sheet surface is within 5 μm. It is a material. If the maximum thickness of the binder is too thick, short circuits and cross leaks of the reaction gas and the electrolytic solution are likely to occur when used in a fuel cell or a redox flow battery.
The above-mentioned porous electrode base material has a thickness of 80 to 300 μm, a bulk density of 0.18 to 0.42 g / cm ³ , a penetration resistance of 3.0 to 7.0 mΩ · cm ² , and transparency in the thickness direction. It is preferable that the air temperature is 0.2 to 7.1 L / (m ² · Pa · s) in terms of performance.
When a coating layer made of carbon powder and a water repellent is formed on at least one surface of the above-mentioned porous electrode base material, it can be used as a gas diffusion layer for a polymer electrolyte fuel cell.
Further, if an electrode catalyst layer is provided on the coating layer of the gas diffusion layer for a polymer electrolyte fuel cell, it can be used as a gas diffusion electrode for a polymer electrolyte fuel cell.

Hereinafter, the present invention will be described in more detail in Examples.
<Calculation of bulk density>
Twenty 3 x 3 cm square test pieces were randomly taken out from the manufactured porous electrode base material, and the thickness of each was measured at 5 points for each sample with a micrometer (manufactured by Mitutoyo) to obtain the average thickness. It was calculated and weighed with an electronic 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 20 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 penetration resistance>
The electrical resistance (penetration resistance) in the thickness direction of the porous electrode base material is such that the porous electrode base material is sandwiched between gold-plated copper plates and pressurized at 1.0 MPa from above and below the copper plate, and a current is applied at a current density of 10 mA / cm ² . The resistance value at the time of flowing was measured and obtained from the following equation. The sample size of the porous electrode base material is 25 mm in diameter.

Penetration resistance (mΩ · cm ² ) = measured resistance value (mΩ) x sample area (cm ² )
<Measurement of air permeability in the thickness direction>
In accordance with JIS standard P-8117, the time required for 200 mL of air to permeate is measured using a Garley densometer, and the air permeability (L / (m ² · Pa · s) is measured from the average value of 10 points. )) Was calculated.
<Measuring method of the maximum thickness of the binder attached to the carbon fiber binding part>
The maximum thickness of the binder attached to the carbon fiber binding portion on the surface of the porous electrode substrate is determined by a scanning electron microscope (SEM). The vicinity of the surface in the cross section of the porous electrode base material cut out arbitrarily is observed at a magnification of 1000 times, and 50 points where the carbon fibers are bonded are extracted. The thickness of the binder existing on the carbon fiber at the binding point was measured by Image Proplus (manufactured by Nippon Roper Co., Ltd.), and the binder thickness was determined by the maximum height among the 20 points.

(Example 1)
<Preparation of porous electrode base material>
As carbon fibers, 100 parts by mass of PAN-based carbon fiber with an average diameter of 7 μm cut to a length of 3 mm and 20 parts by weight of polyvinyl alcohol (PVA) fiber (trade name: VBP105-1, manufactured by Kuraray Co., Ltd.) having a length of 3 mm. , Polyethylene pulp (SWP drainage degree 450 ml manufactured by Mitsui Kagaku Co., Ltd., pulp drainage degree test method of JIS P8121 (1) measured by Canadian standard type) 20 parts by mass was dispersed in water and continuously made on a wire net. After that, it was dried to obtain carbon fiber paper.

100 parts by mass of this carbon fiber paper is impregnated with a methanol solution of phenol resin (trade name: Phenolite J-325, manufactured by DIC Co., Ltd.), and the methanol is sufficiently dried in a heating furnace to reduce the non-volatile content of the phenol resin to 100. A phenol resin impregnated carbon fiber paper adhered by mass was obtained.

This phenol resin-impregnated carbon fiber paper was roll-pressed with a linear force of 8 × 10 ⁴ N / m at a temperature of 250 ° C. to cure the phenol resin. After that, it was continuously carbonized at 1900 ° C. in an inert gas (nitrogen) atmosphere, with a thickness of 190 μm, a bulk density of 0.29 g / cm ³ , a penetration resistance of 4.0 mΩ · cm ² , and a thickness direction. A porous electrode base material having an air permeability of 3.4 L / (m ² · Pa · s) was obtained.

This porous electrode base material is adjusted to the position of a guide roll having a diameter of 200 mm so as to have a holding angle of 5 ° with respect to a roller having a diameter of 40 mm. rice field. The surface to be held by the roller was changed so that both sides of the porous electrode base material were processed, and the process of passing through the roller having a diameter of 40 mm was performed again to wind up. The diameter of the roll used for adjusting the holding angle is 200 mm. Next, the porous electrode base material is unwound and treated with a rotating brush (wire diameter 0.3 mm, rotation speed 200 rpm, 2 rolls on each side so as to be processed in the forward / reverse direction) from both sides, and then the porous electrode base material is applied. Was rolled up. When the maximum thickness of the binder attached to the carbon fiber binding portion on the surface of the obtained porous electrode base material was measured, good results were obtained as shown in Table 1.

<Water repellent treatment of porous electrode base material>
To prepare a water-repellent treatment liquid for a porous electrode substrate, PTFE dispersion (31-JR, manufactured by Mitsui DuPont Fluorochemical), a surfactant (polyoxyethylene (10) octylphenyl ether) and distilled water are used. board. After adjusting the solid content concentration in the water-repellent treatment liquid to 1 wt% for PTFE and 2 wt% for the surfactant, distilled water is added and the mixture is stirred at 1000 rpm for 10 minutes using a disper to repel water. A treatment liquid was prepared.
The porous electrode base material was impregnated by immersing it in the above water-repellent treatment liquid. After the excess water-repellent treatment liquid is removed by passing the impregnated porous electrode base material through two pairs of nip rolls, the porous electrode base material is subjected to the water-repellent treatment by drying in a drying furnace. Got

<Preparation of gas diffusion layer>
Denka Black (manufactured by Denki Kagaku Kogyo Co., Ltd.), ion-exchanged water, and surfactant are mixed at a ratio of 8: 100: 0.8, respectively, and while cooling using Homomixer MARK-II (manufactured by Primix Co., Ltd.). Stirring was performed at 15,000 rpm for 30 minutes to obtain a coating liquid 1.

Polytetrafluoroethylene (PTFE) dispersion was added to the coating liquid 1 at a ratio of 0.3 to carbon black 1, and the mixture was stirred with the dispersion at 5000 rpm for 15 minutes to obtain the coating liquid 2.

The coating liquid 2 was discharged by a slot die, coated at a sheet transport speed of 1 m / min, and immediately dried in a hot air drying oven set at 100 ° C. for 20 minutes. Further, after drying, a gas diffusion layer having a coating layer formed was obtained by performing a sintering treatment at 360 ° C. for 10 minutes in a sintering furnace.

<Manufacturing of gas diffusion electrode and power generation test>
A catalyst layer is formed by applying a catalyst ink composed of catalyst-supported carbon (catalyst: Pt, catalyst-supported amount: 50% by mass), a water repellent, and an ionomer on the surface on which the coating layer of the gas diffusion layer is formed and drying. A gas diffusion electrode was obtained. When the polymer electrolyte membrane Nafion NR211 was sandwiched between the obtained gas diffusion electrodes and hot pressed was performed to prepare a membrane electrode assembly, and then a power generation test was conducted, good results were obtained under all test conditions. The results are summarized in Table 1.

(Example 2)
A porous electrode base material, a gas diffusion layer, and a gas diffusion electrode were obtained in the same manner as in Example 1 except that the holding angle was changed to 30 degrees. As shown in Table 1, good results were obtained for the maximum thickness of the binder attached to the carbon fiber binding portion on the surface of the porous electrode base material and the result of the power generation test of the gas diffusion electrode.

(Example 3)
A porous electrode base material, a gas diffusion layer, and a gas diffusion electrode were obtained in the same manner as in Example 1 except that the holding angle was changed to 180 degrees. As shown in Table 1, good results were obtained for the maximum thickness of the binder attached to the carbon fiber binding portion on the surface of the porous electrode base material and the result of the power generation test of the gas diffusion electrode.

(Example 4)
A porous electrode base material, a gas diffusion layer, and a gas diffusion electrode were obtained in the same manner as in Example 1 except that the diameter of the roller to be held was changed to 150 mm. As shown in Table 1, good results were obtained for the maximum thickness of the binder attached to the carbon fiber binding portion on the surface of the porous electrode base material and the result of the power generation test of the gas diffusion electrode.

(Example 5)
A porous electrode base material, a gas diffusion layer, and a gas diffusion electrode were obtained in the same manner as in Example 2 except that the diameter of the roller to be held was changed to 150 mm. As shown in Table 1, good results were obtained for the maximum thickness of the binder attached to the carbon fiber binding portion on the surface of the porous electrode base material and the result of the power generation test of the gas diffusion electrode.

(Example 6)
A porous electrode base material, a gas diffusion layer, and a gas diffusion electrode were obtained in the same manner as in Example 3 except that the diameter of the roller to be held was changed to 150 mm. As shown in Table 1, good results were obtained for the maximum thickness of the binder attached to the carbon fiber binding portion on the surface of the porous electrode base material and the result of the power generation test of the gas diffusion electrode.

(Example 7)
A porous electrode base material, a gas diffusion layer, and a gas diffusion electrode were obtained in the same manner as in Example 1 except that a base material that did not undergo carbonization was used as the porous electrode base material. As shown in Table 1, good results were obtained for the maximum thickness of the binder attached to the carbon fiber binding portion on the surface of the porous electrode base material and the result of the power generation test of the gas diffusion electrode.

(Example 8)
The grain of carbon fiber paper and the grain of phenol resin are halved, the thickness is 95 μm, the bulk density is 0.22 g / cm ³ , the penetration resistance is 3.8 mΩ · cm ² , and the air permeability in the thickness direction is 3. A porous electrode base material, a gas diffusion layer, and a gas diffusion electrode were obtained in the same manner as in Example 1 except that the porous electrode base material was 4 L / (m ² · Pa · s). As shown in Table 1, good results were obtained for the maximum thickness of the binder attached to the carbon fiber binding portion on the surface of the porous electrode base material and the result of the power generation test of the gas diffusion electrode.

(Example 9)
The grain of carbon fiber paper and the grain of phenol resin are increased by 1.5 times, the thickness of the porous electrode base material is 270 μm, the bulk density is 0.36 g / cm ³ , the penetration resistance is 4.9 mΩ · cm ² , and the thickness. The porous electrode base material, the gas diffusion layer, and the gas diffusion are the same as in Example 1 except that the porous electrode base material having an air permeability of 0.57 L / (m ² · Pa · s) is used. An electrode was obtained. As shown in Table 1, good results were obtained for the maximum thickness of the binder attached to the carbon fiber binding portion on the surface of the porous electrode base material and the result of the power generation test of the gas diffusion electrode.

(Example 10)
The porous electrode base material and the gas diffusion layer were treated in the same manner as in Example 1 except that the treatment was performed with a rubber roll having a hardness of A60 and a metal roll plated with hard chrome at a load of 2 kN instead of the treatment of being held by the rollers. A gas diffusion electrode was obtained. As shown in Table 1, good results were obtained for the maximum thickness of the binder attached to the carbon fiber binding portion on the surface of the porous electrode base material and the result of the power generation test of the gas diffusion electrode.

(Example 11)
The porous electrode base material and the gas diffusion layer were treated in the same manner as in Example 2 except that the treatment was performed with a rubber roll having a hardness of A90 and a metal roll plated with hard chrome at a load of 2 kN instead of the treatment of being held by the rollers. A gas diffusion electrode was obtained. As shown in Table 1, good results were obtained for the maximum thickness of the binder attached to the carbon fiber binding portion on the surface of the porous electrode base material and the result of the power generation test of the gas diffusion electrode.

(Comparative Example 1)
A porous electrode base material, a gas diffusion layer, and a gas diffusion electrode were obtained in the same manner as in Example 1 except that the treatment of holding them on the rollers and the cleaning treatment were not performed. The maximum thickness of the binder attached to the carbon fiber binding portion on the surface of the obtained porous electrode base material was large, and it was confirmed that the initial voltage decreased in the power generation test accordingly.

(Comparative Example 2)
A porous electrode base material, a gas diffusion layer, and a gas diffusion electrode were obtained in the same manner as in Example 8 except that the treatment of holding them on the rollers and the cleaning treatment were not performed. The maximum thickness of the binder attached to the carbon fiber binding portion on the surface of the obtained porous electrode base material was large, and it was confirmed that the initial voltage decreased in the power generation test accordingly.

(Comparative Example 3)
A porous electrode base material, a gas diffusion layer, and a gas diffusion electrode were obtained in the same manner as in Example 9 except that the treatment of holding them on the rollers and the cleaning treatment were not performed. The maximum thickness of the binder attached to the carbon fiber binding portion on the surface of the obtained porous electrode base material was large, and it was confirmed that the initial voltage decreased in the power generation test accordingly.

Claims (9)

A carbon fiber sheet in which carbon fibers are bound by carbon, and a porous electrode base material having a maximum thickness of a binder attached to a carbon fiber bound portion on the sheet surface of 5 μm or less. The thickness of the porous electrode base material according to claim 1 is 80 to 300 μm, the bulk density is 0.18 to 0.42 g / cm ³ , the penetration resistance is 3.0 to 7.0 mΩ · cm ² , and the thickness direction. Gas for a polymer electrolyte fuel cell having an air permeability of 0.2 to 7.1 L / (m ² · Pa · s) and having a coating layer composed of carbon powder and a water repellent on at least one surface. Diffusion layer. The gas diffusion electrode for a polymer electrolyte fuel cell having an electrode catalyst layer on the coating layer of the gas diffusion layer for a polymer electrolyte fuel cell according to claim 2. A solid using the porous electrode base material according to claim 1, the gas diffusion layer for a polymer electrolyte fuel cell according to claim 2, or the gas diffusion electrode for a polymer electrolyte fuel cell according to claim 3. Membrane electrode assembly for polymer electrolyte fuel cells. The method for producing a gas diffusion layer for a polymer electrolyte fuel cell according to claim 2, which comprises the following steps [1] to [6].
Step [1]: The porous electrode base material is held by a roll having a diameter of 40 to 150 mm at an angle of 2 to 180 ° along the sheet flow direction, and is run at a sheet tension of 10 to 100 N / m to be porous. A process of desorbing weakly bonded carbon powder contained in the electrode base material.
Step [2]: The carbon powder on the porous electrode base material obtained in the above step [1] and the excess binder of the carbon fiber binding portion are continuously removed by a rotary brush having a wire diameter of 0.05 mm to 0.3 mm. The process of squeezing.
Step [3]: A step of removing the carbon powder on the porous electrode base material obtained in the above step [2].
Step [4]: A step of forming a coating layer by applying a coating liquid consisting of a conductive agent, a water repellent agent, a surfactant, and water on the porous electrode base material obtained in the above step [3].
Step [5]: A step of heating the coating layer formed on the porous electrode substrate in the above step [4] to 50 to 150 ° C. and drying the coating layer.
Step [6]: A step of heating the porous electrode base material on which the coating layer is formed in the above step [5] to 200 to 400 ° C. and sintering the water repellent to obtain a gas diffusion layer. The method for producing a gas diffusion layer for a polymer electrolyte fuel cell according to claim 5, which comprises the following step [1'] instead of the step [1].
Step [1']: The porous electrode base material is pressed with a rubber roll having a JIS-A rubber hardness of A60 to A100 and a metal roll plated with hard chrome with a load of 1 to 10 kN to obtain the porous electrode. A process of removing weakly bonded carbon powder contained in a base material. The method for producing a polymer electrolyte gas diffusion electrode according to claim 3, further comprising the following step [7] after the steps 5 and 6 [6].
Step [7]: A step of forming an electrode catalyst layer on the gas diffusion layer on which the coating layer is formed. Instead of the step [1], a porous electrode base material is used as a JIS-A rubber hardness A60 to A100.
The present invention comprises a step of desorbing weakly bonded carbon powder contained in the porous electrode base material by pressing the rubber roll and the hard chrome-plated metal roll with a load of 1 to 10 kN. 5. The method for manufacturing a gas diffusion layer for a solid polymer fuel cell according to 5. Instead of the step [1], a porous electrode base material is used as a JIS-A rubber hardness A60 to A100.
The present invention comprises a step of desorbing weakly bonded carbon powder contained in the porous electrode base material by pressing the rubber roll and the hard chrome-plated metal roll with a load of 1 to 10 kN. 6. The method for manufacturing a solid polymer gas diffusion electrode according to 6.