JP5226490B2 - Method for producing porous electrode substrate - Google Patents

Description

  The present invention relates to a method for producing a porous electrode substrate.

The porous electrode substrate is made by impregnating a short carbon fiber papermaking body or nonwoven fabric with a resin composition solution in which a resin composition that is carbonized by heating is dissolved in a solvent, and then removing the solvent to carbonize the resin composition. It is manufactured by doing. Therefore, a large amount of energy is required to remove the solvent.
Patent Document 1 discloses a method in which curved carbon fibers and phenol resin particles are wet-mixed and then heat-pressed and then fired at 1000 ° C., but the loss of phenol resin particles in the paper making process is large. Sufficient conductivity is not obtained.
Patent Document 2 describes a method of using a resin powder instead of a resin composition solution and obtaining a porous electrode substrate without completely melting the resin powder. Although not clear from the literature, there is a drawback that a firm sheet cannot be obtained unless a very large amount of resin powder is used.

Japanese Patent Laid-Open No. 5-78182 JP 2007-273464 A

  It is an object of the present invention to obtain a porous electrode substrate having sufficient conductivity, that is, having a low specific resistance in the thickness direction, without requiring large energy for solvent removal, which was a problem of the prior art. And

The present invention is as follows.
I: A method for producing a porous electrode substrate in which the following steps (A) to (D) are sequentially performed.
(A) The following (1) to (5) are subjected to dispersion papermaking to obtain a papermaking body;
(1) Carbon short fiber 100 parts by mass (2) Binder short fiber 25 to 90 parts by mass (3) Phenol resin particles 540 to 720 having an average particle diameter of 10 to 100 μm made of a novolac type phenol resin having a melting point of 40 to 80 ° C. (4) 60 to 80 parts by mass of particles having an average particle size of 10 to 100 μm made of hexamethylenetetramine (5) 300 to 500 parts by mass of polyethylene pulp having a Canadian freeness of 340 to 680 cc (B) The novolac type phenol resin Heating the paper body at a temperature at which the particles melt but the polyethylene pulp does not melt to melt the novolac phenol resin particles to obtain a paper body coated with polyethylene pulp with the novolac phenol resin;
(C) A step of heating and pressurizing to a temperature above the glass transition point of the resin constituting the polyethylene pulp to obtain a sheet-like material;
(D) The process of carbonizing the novolak-type phenol resin in a sheet-like material, and obtaining a porous electrode base material II: The manufacturing method of the porous electrode base material which performs the following (E)-(H) processes in order.
(E) The following steps (1) to (5) are used for dispersion papermaking to obtain a papermaking body;
(1) Carbon short fiber 100 parts by mass (2) Binder short fiber 25 to 90 parts by mass (3) Phenol resin particles 300 to 400 having an average particle diameter of 10 to 100 μm made of a novolac type phenol resin having a melting point of 40 to 80 ° C. (4) 300 to 400 parts by mass of phenol resin particles having an average particle size of 10 to 100 μm made of a resol type phenol resin (5) 300 to 500 parts by mass of polyethylene pulp having Canadian freeness of 340 to 680 cc (F) The novolak Heating the paper body at a temperature that melts the phenolic resin particles but not the polyethylene pulp to melt the novolac phenolic resin particles to obtain a paper body coated with polyethylene pulp with the phenolic resin;
(G) a step of heating and pressurizing to a temperature equal to or higher than the glass transition point of the resin constituting the polyethylene pulp to obtain a sheet-like material;
(H) A step of carbonizing the phenol resin in the sheet to obtain a porous electrode substrate

  According to the present invention, it is possible to obtain a porous electrode substrate having sufficient conductivity, that is, having a low specific resistance in the thickness direction, without requiring large energy for solvent removal, which was a problem of the prior art. Can do.

[Short carbon fiber]
The average diameter of the short carbon fiber used in the present invention is not particularly limited. For example, about 3-30 micrometers is preferable for surface smoothness and electroconductivity provision of a porous electrode base material, 4-20 micrometers is more preferable, and 4-8 micrometers is more preferable.
The use of two or more types of short carbon fibers having different average diameters is also preferable for achieving both surface smoothness and conductivity of the porous electrode substrate. The length of the carbon short fiber is not particularly limited. In order to increase the dispersibility and the mechanical strength of the porous electrode substrate in the process of obtaining the papermaking body, 3 mm or more and 12 mm or less are preferable, and 3 mm or more and 9 mm or less are more preferable.
The type of carbon fiber is not particularly limited, and for example, polyacrylonitrile (PAN) -based carbon fiber, pitch-based carbon fiber, phenol resin-based carbon fiber, regenerated cellulose-based carbon fiber, cellulose-based carbon fiber, etc. should be used. Can do. These carbon fibers can be used alone or in combination of two or more. In particular, PAN-based carbon fibers are preferable because of their high compressive strength and tensile strength.

[Binder short fiber]
The binder short fibers used in the present invention can be dispersed together with the carbon short fibers during the process of obtaining the papermaking body, and the carbon short fibers can be held together as a papermaking body. There is no particular limitation as long as short carbon fibers can be bound together by pressure. Polyvinyl alcohol (PVA) short fibers are preferred from the viewpoints of handleability and binding properties.
In order to obtain a solid papermaking body, the amount of the binder short fibers is 25 to 90 parts by mass with respect to 100 parts by mass of the carbon short fibers. More preferably, it is 30-80 mass parts, and it is especially preferable that it is 50-80 mass parts.

[Novolac type phenolic resin particles]
The melting point of the novolac type phenol resin constituting the novolac type phenol resin particles used in the present invention is 40 to 80 ° C. More preferably, it is 50-70 degreeC, and it is especially preferable that it is 55-65 degreeC.
When the melting point is 80 ° C. or lower, the novolac type phenol resin particles can be sufficiently melted during the moisture drying after the wet papermaking as a step of obtaining the papermaking body. On the other hand, if the melting point is 40 ° C. or higher, the papermaking bodies can be handled without fusing at room temperature.
The average particle size of the novolac type phenol resin particles is 10 to 100 μm in consideration of handling property and capture property to polyethylene pulp. More preferably, it is 20-60 micrometers, and it is especially preferable that it is 30-50 micrometers.

[Hexamethylenetetramine particles]
Hexamethylenetetramine constituting the hexamethylenetetramine particles used in the present invention serves as a thermosetting agent for novolak-type phenolic resins. The average particle diameter of the hexamethylenetetramine particles is 10 to 100 μm in consideration of the handling property and the trapping property to polyethylene pulp, and the miscibility with the novolac type phenol resin particles. More preferably, it is 20-60 micrometers, and it is especially preferable that it is 30-50 micrometers.
When using novolac-type phenol resin particles and hexamethylenetetramine particles, the charge amount of novolac-type phenol resin particles is based on 100 parts by mass of carbon short fibers so that polyethylene pulp can be sufficiently coated in the subsequent heating step. 540 to 720 parts by mass. It is more preferable that it is 630-720 mass parts. The charged amount of hexamethylenetetramine particles is 60 to 80 parts by mass with respect to 100 parts by mass of carbon short fibers in order for the novolac type phenol resin particles to be effectively cured. More preferably, it is 70-80 mass parts.
The method for mixing the hexamethylenetetramine particles is not particularly limited, but may be pulverized together with the novolac type phenol resin using a normal pulverizer, or may be mixed after pulverizing the novolac type phenol resin.
For example, phenol resin particles B (trade name: Resitop PG-4130, manufactured by Gunei Chemical Industry Co., Ltd.) contain about 10 mass% hexamethylenetetramine.

[Resol type phenolic resin particles]
The resol type phenol resin constituting the resol type phenol resin particles used in the present invention serves as a thermosetting agent for the novolak type phenol resin. The average particle diameter of the resol type phenol resin particles is 10 to 100 μm in consideration of the handling property and the trapping property to the polyethylene pulp, and the miscibility with the novolac type phenol resin particles. More preferably, it is 20-60 micrometers, and it is especially preferable that it is 30-50 micrometers.
When using novolak-type phenol resin particles and resol-type phenol resin particles, the charge amount of novolak-type phenol resin particles is 100 parts by mass of carbon short fibers so that polyethylene pulp can be sufficiently coated in the subsequent heating step. 300 to 400 parts by mass. It is more preferable that it is 350-400 mass parts. The charged amount of the resol type phenol resin particles is 300 to 400 parts by mass with respect to 100 parts by mass of the short carbon fibers so that the novolac type phenol resin particles are effectively cured. It is more preferable that it is 350-400 mass parts. The mixing method is not particularly limited, but may be pulverized with the novolac type phenol resin by using a normal pulverizer, or may be mixed after pulverizing the novolac type phenol resin.
For example, phenol resin particles A (trade name: Resitop PGA-2165, manufactured by Gunei Chemical Industry Co., Ltd.) contain about 50% by mass of a resol type phenol resin.

[Polyethylene pulp]
The polyethylene pulp used in the present invention has a Canadian freeness of 340 to 680 cc. It is particularly preferably 340 to 580 cc. By using polyethylene pulp having a Canadian freeness of 340 cc or more, sufficient drainage is secured, and a paper body in which novolak type phenol resin particles are uniformly dispersed is obtained. In addition, by using polyethylene pulp having a Canadian freeness of 680 cc or less, novolac-type phenol resin particles that can be sufficiently coated with polyethylene pulp in a subsequent drying step are captured.
The Canadian freeness value is also an index of filtration performance related to entanglement of fibers due to fiber branching. The Canadian freeness value is a value measured according to JISP8121 “Pulp Freeness Test Method; Canadian Standard Type”.
The amount of the polyethylene pulp charged is 300 to 100 parts by mass of the short carbon fiber in order to bind the short carbon fiber sufficiently in the subsequent heating and pressurizing step and to give sufficient conductivity by the carbonization step. 500 parts by mass. It is more preferable that it is 400-500 mass parts.
In the present invention, polyethylene pulp and novolac type phenol resin particles are used in combination because novolak type phenol resin particles are mixed with polyethylene pulp, and after a heating step, novolac type phenol resin is coated with polyethylene pulp and the residual carbon ratio is increased. This is because a porous electrode substrate that is improved and finally has sufficient mechanical strength is obtained.
When only polyethylene pulp is used, the residual carbon ratio is remarkably low, so that it disappears in the subsequent carbonization step, and only a porous electrode substrate having poor mechanical strength can be obtained.
If polyethylene pulp is not used, there is no binding between short carbon fibers by polyethylene pulp coated with a phenol resin in the subsequent step, and thus a solid sheet cannot be obtained.
On the other hand, when polyethylene pulp and thermosetting phenol resin particles are used in combination, the thermosetting phenol resin also softens once as the temperature rises from room temperature, but starts to harden almost without flowing. Therefore, polyethylene pulp cannot be coated with thermosetting phenolic resin, and the residual carbon ratio remains low.

[Step of melting the novolac-type phenol resin particles by heating]
The heating temperature of the paper body is a temperature at which the novolac type phenol resin particles melt but the polyethylene pulp does not melt. More specifically, it is preferably 65 to 90 ° C, more preferably 65 to 80 ° C, and particularly preferably 70 to 80 ° C. As a result, a carbon fiber paper in which polyethylene pulp is coated with a novolak type phenol resin is obtained, and a high bulk density porous electrode base material in which the form of polyethylene pulp is replicated by a subsequent carbonization treatment is obtained. In this temperature range, almost no thermosetting reaction occurs with hexamethylenetetramine or resol type phenol resin.

[Heating and pressing process]
The heating and pressing temperature for obtaining a sheet from the carbon fiber paper is not less than the temperature of the glass transition point of polyethylene. The heating temperature is preferably in the range of 90 to 180 ° C, more preferably in the range of 135 to 180 ° C, and particularly preferably in the range of 160 to 180 ° C. By setting the heating and pressing temperature to be equal to or higher than the glass transition point of polyethylene, the polyethylene pulp coated with the novolac type phenol resin is sufficiently softened, and the short carbon fibers can be bound. Further, at 120 ° C. or higher, the thermosetting reaction with hexamethylenetetramine or resol type phenol resin proceeds rapidly, so that the residual carbon ratio of the novolak type phenol resin is improved in the subsequent carbonization step. Moreover, it is preferable that the heating temperature be 180 ° C. or less because the possibility that the phenol resin is rapidly cured and cracked or peeled off from the short carbon fiber is reduced.
The heating and pressing pressure is not particularly limited by the present invention as long as it is within a pressure range in which a sheet having a uniform thickness can be obtained.

[Carbonization process]
The sheet carbonization method may be any method in which the novolak type phenol resin remaining uncured at the time of heating and pressurization is completely cured by continuous temperature rise from room temperature and then carbonized continuously, and is inert. It is preferable to carry out in the temperature range of 800-2400 degreeC under atmosphere. Moreover, you may pre-process in the temperature range of 300-800 degreeC by inert atmosphere before the said carbonization. By performing the pretreatment, it is preferable because the decomposition gas generated in the initial stage of carbonization can be sufficiently discharged, and the adhesion and deposition of decomposition products on the inner wall of the carbonization furnace can be suppressed.

Hereinafter, the present invention will be described more specifically with reference to examples. Each physical property in the examples was measured by the following method.
(1) Thickness The thickness of the porous electrode substrate was measured using a thickness measuring device dial thickness gauge 7321 (manufactured by Mitutoyo Corporation). The size of the probe was 10 mm in diameter, and the measurement pressure was 1.5 kPa.
(2) Specific resistance in the thickness direction The specific resistance in the thickness direction of the porous electrode substrate is determined by sandwiching a sample between gold-plated copper plates, pressurizing at 1 MPa from the top and bottom of the gold-plated 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.
Specific resistance in thickness direction (Ωcm) = measured resistance value (Ω) × sample area (cm ² ) / sample thickness (cm)
(3) Average particle diameter The average particle diameter of the particles was determined from the number average of about several thousand circumscribed circle equivalent diameters by analyzing the particle image using a morphological observation photograph taken with a scanning electron microscope.

[Example 1]
A fiber bundle of polyacrylonitrile (PAN) -based carbon fibers having an average fiber diameter of 7 μm was cut to obtain short fibers having an average fiber length of 3 mm. Next, 100 mass parts of this short fiber bundle was opened in water and when sufficiently dispersed, polyvinyl alcohol (PVA) short fibers having an average fiber length of 3 mm (trade name: VBP105-1, manufactured by Kuraray Co., Ltd.) 80 Mass parts, phenol resin particles A (trade name: Resitop PGA-2165, manufactured by Gunei Chemical Industry Co., Ltd.), and Canadian freeness 340 cc polyethylene pulp (trade name: SWP-E620, manufactured by Mitsui Chemicals, Inc.) 500 parts by mass were uniformly dispersed, and paper making was performed using a standard square sheet machine (manufactured by Kumagai Riki Kogyo Co., Ltd.). Here, the use of 800 parts by mass of phenol resin particles A means that 400 parts by mass of novolac type phenol resin particles having a melting point of 65 ° C. and an average particle size of about 30 μm and resol type phenol resin particles 400 having an average particle size of about 30 μm. This corresponds to the use of mass parts.
The obtained paper body was dried with a roll dryer heated to 80 ° C. to obtain a carbon fiber paper having a mass per unit area of 107 g / m ² .
Two sheets of the carbon fiber paper were stacked and sandwiched between release papers, placed in a batch press apparatus at 180 ° C. and 8 MPa for 3 minutes, and then the press pressure was released and the sheet was naturally cooled to room temperature to obtain a sheet. In FIG. 1, the surface observation photograph by the scanning electron microscope of the obtained sheet | seat is shown.
Subsequently, the said sheet | seat was heated at 2000 degreeC by the batch carbonization furnace for 1 hour in nitrogen gas atmosphere, and the porous electrode base material was obtained by carbonizing. FIG. 2 shows a surface observation photograph by a scanning electron microscope. The obtained porous electrode substrate had a mass per unit area of 55 g / m ² , a thickness of 160 μm, and a specific resistance in the thickness direction under a load of 1.0 MPa of 0.51 Ω · cm.

[Example 2]
Mass per unit area in the same manner as in Example 1 except that 800 parts by mass of phenol resin particles A was 800 parts by mass of phenol resin particles B (trade name: Resitop PG-4130, manufactured by Gunei Chemical Industry Co., Ltd.). Obtained a carbon fiber paper of 124 g / m ² . Here, 800 parts by mass of the phenol resin particles B are 720 parts by mass of novolac-type phenol resin particles having a melting point of 56 ° C. and an average particle diameter of about 30 μm, and 80 parts by mass of hexamethylenetetramine particles having an average particle diameter of about 30 μm. Corresponding to
Further, in the same manner as in Example 1, the porous electrode substrate had a mass per unit area of 74 g / m ² , a thickness of 190 μm, and a specific resistance in the thickness direction of 0.52 Ω · cm under a load of 1.0 MPa. Got.

Example 3
The mass per unit area was 113 g / m ^{2 in} the same manner as in Example 1 except that the polyethylene pulp was a Canadian freeness 540 cc polyethylene pulp (trade name: SWP-EST-8, manufactured by Mitsui Chemicals, Inc.). Carbon fiber paper was obtained. Further, in the same manner as in Example 1, the porous electrode substrate had a mass per unit area of 61 g / m ² , a thickness of 169 μm, and a specific resistance in the thickness direction of 0.46 Ω · cm under a load of 1.0 MPa. Got.

Example 4
Carbon fiber paper having a mass per unit area of 128 g / m ² was obtained in the same manner as in Example 3 except that the phenol resin particles A were changed to the phenol resin particles B. Further, in the same manner as in Example 1, the porous electrode substrate has a mass per unit area of 79 g / m ² , a thickness of 194 μm, and a specific resistance in the thickness direction of 0.48 Ω · cm under a load of 1.0 MPa. Got.

Example 5
A carbon fiber having a mass per unit area of 106 g / m ^{2 in} the same manner as in Example 1 except that the polyethylene pulp was a Canadian freeness 580 cc polyethylene pulp (trade name: SWP-E400, manufactured by Mitsui Chemicals, Inc.). I got paper. Further, in the same manner as in Example 1, the porous electrode substrate has a mass per unit area of 54 g / m ² , a thickness of 161 μm, and a specific resistance in the thickness direction of 0.52 Ω · cm under a load of 1.0 MPa. Got.

Example 6
Carbon fiber paper having a mass per unit area of 120 g / m ² was obtained in the same manner as in Example 5 except that the phenol resin particles A were changed to the phenol resin particles B. Further, in the same manner as in Example 1, the porous electrode substrate had a mass per unit area of 71 g / m ² , a thickness of 187 μm, and a specific resistance in the thickness direction of 0.58 Ω · cm under a load of 1.0 MPa. Got.

Example 7
Carbon fiber having a mass per unit area of 97 g / m ^{2 in} the same manner as in Example 1 except that the polyethylene pulp was a Canadian freeness 680 cc polyethylene pulp (trade name: SWP-E790, manufactured by Mitsui Chemicals, Inc.). I got paper. Further, in the same manner as in Example 1, the porous electrode substrate had a mass per unit area of 46 g / m ² , a thickness of 167 μm, and a specific resistance in the thickness direction of 0.64 Ω · cm under a load of 1.0 MPa. Got.

Example 8
Carbon fiber paper having a mass per unit area of 119 g / m ² was obtained in the same manner as in Example 7 except that the phenol resin particles A were changed to the phenol resin particles B. Further, in the same manner as in Example 1, the porous electrode substrate has a mass per unit area of 71 g / m ² , a thickness of 270 μm, and a specific resistance in the thickness direction of 0.71 Ω · cm under a load of 1.0 MPa. Got.

[Comparative example 1] (Comparative example in which the amount of phenol resin particles A charged is small)
Carbon fiber paper having a mass per unit area of 87 g / m ² was obtained in the same manner as in Example 1 except that the amount of the phenol resin particles A charged was 400 parts by mass.
Here, using 400 parts by mass of phenol resin particles A corresponds to using 200 parts by mass of novolac type phenol resin particles and 200 parts by mass of resol type phenol resin particles.
Further, in the same manner as in Example 1, the porous electrode substrate had a mass per unit area of 40 g / m ² , a thickness of 161 μm, and a specific resistance in the thickness direction of 1.11 Ω · cm under a load of 1.0 MPa. Got.

[Comparative Example 2] (Comparative example in which the amount of polyethylene pulp and phenol resin particles A charged is small) Example except that the amount of polyethylene pulp charged is 250 parts by mass and the amount of phenol resin particles A is 200 parts by mass. In the same manner as in Example ¹ , carbon fiber paper having a mass per unit area of 48 g / m ² was obtained.
Here, using 200 parts by mass of the phenol resin particles A corresponds to using 100 parts by mass of novolac type phenol resin particles and 100 parts by mass of resol type phenol resin particles.
Further, in the same manner as in Example 1, the porous electrode substrate had a mass per unit area of 28 g / m ² , a thickness of 149 μm, and a specific resistance in the thickness direction of 1.48 Ω · cm under a load of 1.0 MPa. Got.

[Comparative Example 3] (Comparative Example with a small charge of polyethylene pulp and phenol resin particles B)
Carbon fiber paper having a mass per unit area of 51 g / m ² was obtained in the same manner as in Example 2 except that the amount of polyethylene pulp charged was 250 parts by mass and the amount of phenol resin particles B was 200 parts by mass. Obtained. Here, 200 parts by mass of phenol resin particles B use 180 parts by mass of novolac type phenol resin particles having a melting point of 56 ° C. and an average particle diameter of about 30 μm, and 20 parts by mass of hexamethylenetetramine particles having an average particle diameter of about 30 μm. Corresponding to
Further, in the same manner as in Example 1, the porous electrode substrate had a mass per unit area of 30 g / m ² , a thickness of 138 μm, and a specific resistance in the thickness direction of 1.29 Ω · cm under a load of 1.0 MPa. Got.

[Comparative Example 4] (Comparative example using thermosetting phenol resin particles C)
Units were obtained in the same manner as in Example 1 except that the phenol resin particles were thermosetting phenol resin particles C (trade name: Marilyn FM-150, manufactured by Gunei Chemical Industry Co., Ltd.) having an average particle size of about 150 μm. Carbon fiber paper having a mass per area of 137 g / m ² was obtained. Further, in the same manner as in Example 1, the porous electrode substrate has a mass per unit area of 82 g / m ² , a thickness of 205 μm, and a specific resistance in the thickness direction of 0.59 Ω · cm under a load of 1.0 MPa. However, it was brittle and easily buckled by the load.
Table 1 shows the physical properties of the carbon fiber paper and the porous electrode substrate.

  The porous electrode base materials obtained by carbonization of Examples 1 to 8 had a low specific resistance in the thickness direction.

  The porous electrode substrate according to the present invention is particularly suitable as a gas diffuser for fuel cells, but is not limited to this, and can be applied to electrode substrates for various batteries. However, it is not limited to these.

2 is a surface observation photograph of the sheet obtained in Example 1 with a scanning electron microscope. 2 is a surface observation photograph of the porous electrode substrate obtained in Example 1 with a scanning electron microscope.

Claims (2)

The manufacturing method of the porous electrode base material which performs the following (A)-(D) processes in order.
(A) The following (1) to (5) are subjected to dispersion papermaking to obtain a papermaking body;
(1) Carbon short fiber 100 parts by mass (2) Binder short fiber 25 to 90 parts by mass (3) Phenol resin particles 540 to 720 having an average particle diameter of 10 to 100 μm made of a novolac type phenol resin having a melting point of 40 to 80 ° C. (4) 60 to 80 parts by mass of particles having an average particle size of 10 to 100 μm made of hexamethylenetetramine (5) 300 to 500 parts by mass of polyethylene pulp having a Canadian freeness of 340 to 680 cc (B) The novolac type phenol resin Heating the paper body at a temperature at which the particles melt but the polyethylene pulp does not melt to melt the novolac phenol resin particles to obtain a paper body coated with polyethylene pulp with the novolac phenol resin;
(C) A step of heating and pressurizing to a temperature above the glass transition point of the resin constituting the polyethylene pulp to obtain a sheet-like material;
(D) Step of obtaining a porous electrode substrate by carbonizing the novolac type phenol resin in the sheet-like material The manufacturing method of the porous electrode base material which performs the following (E)-(H) processes in order.
(E) The following steps (1) to (5) are used for dispersion papermaking to obtain a papermaking body;
(1) Carbon short fiber 100 parts by mass (2) Binder short fiber 25 to 90 parts by mass (3) Phenol resin particles 300 to 400 having an average particle diameter of 10 to 100 μm made of a novolac type phenol resin having a melting point of 40 to 80 ° C. (4) 300 to 400 parts by mass of phenol resin particles having an average particle size of 10 to 100 μm made of a resol type phenol resin (5) 300 to 500 parts by mass of polyethylene pulp having Canadian freeness of 340 to 680 cc (F) The novolak Heating the paper body at a temperature that melts the phenolic resin particles but not the polyethylene pulp to melt the novolac phenolic resin particles to obtain a paper body coated with polyethylene pulp with the phenolic resin;
(G) a step of heating and pressurizing to a temperature equal to or higher than the glass transition point of the resin constituting the polyethylene pulp to obtain a sheet-like material;
(H) A step of carbonizing the phenol resin in the sheet to obtain a porous electrode substrate

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