JP5484777B2 - Porous electrode substrate and method for producing the same - Google Patents

Description

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

The solid polymer fuel cell has a polymer electrolyte membrane that selectively conducts hydrogen ions (protons). In addition, a gas diffusion electrode having a catalyst layer mainly composed of carbonaceous powder supporting a noble metal catalyst and a porous electrode substrate was bonded to both surfaces of the polymer electrolyte membrane with the catalyst layer side inside. It has a structure.
Such a joined body composed of a polymer electrolyte membrane and two gas diffusion electrodes is called a membrane-electrode assembly (MEA). In addition, separators having gas flow paths for supplying fuel gas or oxidizing gas and discharging generated gas and excess gas are installed on both outer sides of the MEA.
The porous electrode substrate mainly has the following three functions. The first function is to uniformly supply the fuel gas or the oxidizing gas to the noble metal catalyst in the catalyst layer from the gas flow path formed in the separator disposed outside the porous electrode substrate. The second function is to discharge water produced by the reaction in the catalyst layer. The third function is to conduct electrons necessary for the reaction in the catalyst layer or generated electrons to the separator.

  As a porous electrode base material used in a polymer electrolyte fuel cell, a sheet-like intermediate base material is obtained by making a mixture with a paper making medium containing short carbon fibers, and then the intermediate base material is heated to produce carbon. Resin, for example, resol type phenolic resin, which is thermosetting resin, and the intermediate base material impregnated with phenolic resin is heated to carbonize the phenolic resin, thereby carbonizing short carbon fibers with each other. The base material bound by is used. However, the base material produced by such a method is such that the phenol resin that binds the short carbon fibers shrinks when cured and carbonized, leaving a gap between the short carbon fibers and the resin carbonized product, Since the resin carbonized material is cracked, sufficient conductivity cannot be obtained. Further, when using a porous electrode base material in a polymer electrolyte fuel cell, it is common to perform a water repellent treatment by impregnation or coating with a water repellent such as polytetrafluoroethylene (PTFE). However, at this time, since the insulating water repellent penetrates and accumulates in cracks and gaps in the resin carbonized product, there is a problem that the conductivity of the porous electrode substrate is further remarkably lowered.

  In order to solve such a problem, for example, Patent Document 1 discloses a method for producing a porous electrode substrate using a resin composition in which a novolac type phenol resin N and a resol type phenol resin R are mixed. Since N is thermoplastic and has fluidity even at the curing temperature of R, it suppresses shrinkage when the resin composition is cured. Furthermore, since N is graphitizable and has fluidity at the carbonization temperature, it also suppresses shrinkage when the resin composition is carbonized. Therefore, it is necessary to use a resin composition in which N and R are mixed in order to bind the resin carbonized product to the short carbon fibers without gaps or cracks. The mixing ratio of N and R is also shown in the same document and Patent Document 2, but the fluidity of the resin composition largely depends on the softening point of N and the solution viscosity of R, so these physical properties are ignored. It is not sufficient to specify a simple mixing ratio. For example, even when N having a high softening point or R having a high solution viscosity is used even within the range of the mixing ratio shown in the above document, sufficient fluidity is not exhibited and the resin composition is cured. Cracks. That is, in order to obtain a porous electrode base material in which the carbonized carbon resin binds short carbon fibers without gaps or cracks, an optimum N softening point range and R solution viscosity range must be defined.

Japanese Patent Publication No. 8-18882 Japanese Patent No. 4051714

  The present invention is a porous electrode base material in which a phenol resin carbonized material is bonded to short carbon fibers without gaps or cracks, and has a high conductivity in the thickness direction. An object of the present invention is to provide a porous electrode base material that has minimal gas permeability and further has high gas permeability at a lower cost than conventional ones.

The present invention for solving the above-described problems has the following configuration.
(1) A short carbon fiber aggregate dispersed in a plane has a novolac type phenolic resin N having a softening point of 75 to 95 ° C. measured by the ring and ball method and an apparent viscosity of 50 to 140 mPa · s measured by a B type viscometer. The resin composition obtained by mixing a 60 wt% methanol solution of the resol type phenolic resin R, which is s, with a solid content mass ratio of N: R = 80: 20 to 85:15 is obtained with respect to 100 parts by mass of the carbon fiber. Impregnating the composition to 70 to 130 parts by mass to obtain an intermediate substrate;
Heating the intermediate substrate to carbonize the resin composition;
The manufacturing method of the porous electrode base material which has this.
(2) A step of immersing the porous electrode substrate obtained by the production method described in (1) above in a polytetrafluoroethylene dispersion having a solid content of 5 to 30% by weight;
Further drying and sintering polytetrafluoroethylene to the porous electrode substrate;
The manufacturing method of the porous electrode base material which has this.
(3) The specific resistance increase ΔR [Ω · cm] and the specific resistance increase rate S [%] in the thickness direction after the water repellent treatment before the water repellent treatment satisfy the relationship of ΔR ≦ 0.1 and S ≦ 25. A porous electrode substrate produced by the production method according to claim 2.

  According to the present invention, a porous electrode substrate in which a phenol resin carbonized material is bonded to short carbon fibers without gaps or cracks and has a high conductivity in the thickness direction. It is possible to provide a porous electrode base material that has minimal gas permeability and further has high gas permeability at a lower cost than the conventional one.

2 is a surface observation photograph of the porous electrode substrate obtained in Example 1 with a scanning electron microscope. 2 is a surface observation photograph of the porous electrode substrate obtained in Comparative Example 1 with a scanning electron microscope. 6 is a surface observation photograph of a water-repellent treated porous electrode substrate obtained in Example 5 using a scanning electron microscope.

[Aggregates of short carbon fibers dispersed in a plane]
In the present invention, the short carbon fiber aggregate dispersed in the plane is not limited to a specific thickness or size, and includes non-woven fabrics, paper bodies, felts, cloths and the like whose main constituents are carbon short fibers. Moreover, those manufacturing methods are not specifically limited, For example, you may entangle a fiber by a water jet process, a steam jet process, etc. In particular, a paper body formed by aggregating a plurality of carbon short fibers is preferable, has a high surface smoothness, good electrical contact, and a plurality of carbon shorts that reduce short circuit due to sticking to the polymer electrolyte membrane. A paper body made of aggregated fibers is more preferable.

[Short carbon fiber]
Although the average diameter of the short carbon fiber used in the present invention is not particularly limited, for example, it is preferably about 3 to 30 μm, more preferably 4 to 20 μm, and further preferably 4 to 8 μm for imparting surface smoothness and conductivity. preferable. It is also preferable to use two or more types of short carbon fibers having different average diameters in order to achieve both surface smoothness and conductivity. The length of the short carbon fibers is not particularly limited, but is preferably 3 mm or more and 12 mm or less, and more preferably 3 mm or more and 9 mm or less in order to improve the dispersibility during papermaking and the mechanical strength.
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.

[Novolac type phenolic resin]
The novolak type phenolic resin used in the present invention has a lower softening point than a general novolac type phenolic resin (softening point of 100 ° C. or higher), and has a softening point measured by the ring and ball method (JIS K5601-2-2). 75-95 ° C. More preferably, it is 75-90 degreeC, and it is especially preferable that it is 75-85 degreeC. When the softening point is 95 ° C. or lower, molding processing at a lower temperature than before can be performed, and utility costs in the manufacturing process can be reduced. Further, when the softening point is 75 ° C. or higher, it can be handled without fusing at room temperature.

[Resol type phenolic resin]
The resol-type phenol resin used in the present invention is preferably produced using a catalyst that does not contain a metal that causes a decrease in proton conductivity of the solid polymer electrolyte. As such a resol-type phenol resin, ammonia There are catalytic resol type phenolic resins. The apparent viscosity of a resol type phenolic resin is not easy to say because it easily changes depending on the type of solvent and the solid content concentration, but if it is a methanol solution with a solid content concentration of 60 wt%, it will be handled well in the subsequent resin impregnation step. In order to control the resin adhesion amount while maintaining the properties, the value measured with a B-type viscometer in accordance with JIS K7117-1 is 50 to 140 mPa · s.

(Resin composition)
The mixing ratio of the novolak-type phenol resin N and the resol-type phenol resin R can be appropriately set in order to control the fluidity of the resin composition, but the solid content mass ratio is N: R = 80: 20 to 85:15. By setting the N ratio to 80% or more, the gas permeability and conductivity of the obtained porous electrode substrate are remarkably improved as compared with the case where R is used alone. Further, by setting the N ratio to 85% or less, the residual carbon ratio does not become too low, and the mechanical strength and conductivity can be maintained. Here, the residual carbon ratio is a mass ratio of the resin carbonized material when the solid content mass of the original resin composition is 100%, and is an index representing the degree of carbonization. Generally, the residual carbon rate of R alone is about 50 to 60%, and the residual carbon rate of N alone is about 20 to 30%. The N ratio of the resin composition of the present invention is as high as 80 to 85%, and therefore the residual carbon ratio is lower than that of the resin composition shown in the prior art. From the viewpoint of sufficiently securing the binding area and the number of binding points after carbonization, the amount of the resin composition attached to the short carbon fiber aggregate is 70 to 130 parts by mass with respect to 100 parts by mass of carbon fibers, preferably 70-100 mass parts is good.

[Step of impregnating resin composition to obtain intermediate substrate]
Examples of a method for obtaining an intermediate base material by impregnating the carbon short fiber aggregate with the resin composition include a method of uniformly coating a resin on the surface of the carbon short fiber aggregate using a coater, and dip- The nip method or the method of transferring the resin film to the carbon short fiber aggregate by overlapping the carbon short fiber aggregate and the resin film is known. The method of uniformly impregnating the carbon short fiber aggregate with the resin composition The present invention is not particularly limited by the present invention.

[Step of heating the intermediate substrate to carbonize the resin composition]
As a method of carbonizing the resin composition by heating the intermediate substrate, any method may be used as long as it is completely cured by continuous temperature increase from room temperature and then carbonized continuously, under an inert atmosphere. It is preferable to carry out in the temperature range of 800-2400 degreeC. Moreover, you may pre-process in the temperature range of 300-800 degreeC by inert atmosphere. 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. Furthermore, you may heat-press in a temperature range of 150-300 degreeC before the process at 300-2400 degreeC. Since the resin composition is cured to some extent by the heat and pressure treatment, it is preferably performed from the viewpoint of controlling the thickness of the substrate. The heat and pressure treatment may be performed by stacking two or more intermediate base materials. The pressure and time required for heating and pressurization are not particularly limited by the present invention as long as they are within the pressure range and time range in which a sheet having a uniform thickness can be obtained.

[Water repellent treatment process]
In the polymer electrolyte fuel cell, water as an electrode reaction product and water penetrating the polymer electrolyte membrane are generated on the cathode side. On the anode side, humidified fuel is supplied to suppress drying of the polymer electrolyte membrane. From such points, the porous electrode substrate of the present invention is subjected to water repellent treatment with a water repellent polymer in order to ensure gas permeability. Examples of the water-repellent polymer include polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, which are chemically stable and have high water repellency. It is preferable to use a fluororesin such as coalescence (PFA).
As a method of water-repellent treatment to the porous electrode substrate, a dip method in which the porous electrode substrate is immersed in a dispersion aqueous solution (dispersion) in which fine particles of water-repellent polymer are dispersed, a spray method in which the dispersion aqueous solution is sprayed However, a dipping method with a high uniformity of the introduction amount in the in-plane direction and the thickness direction is preferable. The PTFE dispersion concentration used in the dip method is not particularly limited, but is preferably about 5 to 30% by weight in order to uniformly deposit PTFE without filling the voids of the porous electrode substrate. 10-30 weight% is more preferable, and 15-25 weight% is especially preferable.
The temperature at which PTFE is sintered to the porous electrode substrate must be within a temperature range in which PTFE softens and binds to carbon short fibers or resin carbonized products, and PTFE does not thermally decompose. 300-390 degreeC is more preferable, and 330-360 degreeC is especially preferable.

The water-repellent treatment is a treatment necessary for imparting water repellency to the porous electrode substrate, and the water-repellent polymer that is insulating covers the surface of the porous electrode substrate (a) b) The specific resistance in the thickness direction after the water-repellent treatment is increased as compared with that before the water-repellent treatment by being deposited in the cracks of the resin carbonized material or in the gaps with the short carbon fibers. The porous electrode substrate obtained in the present invention has no cracks in the resin carbonized product and no gaps with the short carbon fibers, that is, no influence of the above (b), so that an increase in specific resistance can be minimized. Regarding the specific resistance in the thickness direction of the porous electrode substrate of the present invention, the value after the water repellent treatment is R ₂ , the value before the water repellent treatment is R ₁ , and the difference is the specific resistance increase ΔR = R ₂ − Assuming R ₁ [Ω · cm], the range of ΔR is ΔR ≦ 0.1, and when the specific resistance increase rate S [%] is defined as S = ΔR / R ₁ × 100, the range of S is S ≦ 25 It is.

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.
-Softening point of novolac type phenol resin The softening point of the novolak type phenol resin in the present invention is measured according to the ring and ball method defined in JIS K5601-2-2, and is a ring and ball automatic softening point tester (trade name: ASP- MG2, manufactured by Meitec Co., Ltd.) was used, and the measurement was performed under the following measurement conditions.
Ring: Brass shoulder ring with an inner diameter of 16 mm and a depth of 6.4 mm Ball: Steel ball with a diameter of 9.5 mm and a weight of 3.5 g Temperature: The temperature of the liquid bath was increased at 5 ° C./min.
-Apparent viscosity of resol type phenol resin methanol solution The measurement of the resol type phenol resin methanol solution (solid content concentration 60 wt%) in the present invention is based on JIS K7117-1, and is a B type viscometer (trade name: BII type viscometer). , Manufactured by Toki Sangyo Co., Ltd.), the rotational speed of the M rotor (No. 1) was 30 rpm, and the temperature was 25 ° C.
-Thickness The thickness of the porous electrode substrate was measured using a thickness measuring device (trade name: 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.
(4) Specific resistance in the thickness direction 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 (Ω · cm) = measured resistance value (Ω) × sample area (cm ² ) / sample thickness (cm)
(5) Gas permeability coefficient in the thickness direction The gas permeability coefficient in the thickness direction of the porous electrode base material is based on JIS P8117, using a Gurley type densometer (manufactured by Kumagai Riki Kogyo Co., Ltd.), The time required for 200 mL of gas (air) to pass through a jig having a diameter of 2 mmφ (compressed part area 0.0314 cm ² ) was measured and calculated from the following equation.
Permeability coefficient (mL · mm / cm ² / hr / mmAq) = Air permeability (mL / cm ² / hr / mmAq) × Sample thickness (mm)

The absolute value of the gas permeability coefficient of the porous electrode substrate greatly depends on the composition of the original carbon fiber paper, the porosity, and the like. In order to quantitatively evaluate the influence of the change of the resin on the increase / decrease of the gas permeability coefficient, the gas permeability coefficient of the porous electrode substrate produced using the resin composition defined in the present invention is defined as P _M , resol type phenol. the gas permeability coefficient was produced using the resin alone porous electrode substrate to define the following equation as P _{R.
P =} P M / P _R
If P> 1, it means that the gas permeability coefficient of the porous electrode substrate has increased due to the resin change, and if P <1, it means that the gas permeability coefficient has decreased. The P _R value, the value obtained in Comparative Example 1 in the case of using the carbon fiber paper A, in the case of using the carbon fiber paper B was used as the values obtained in Comparative Example 3.

As carbon fiber paper, carbon fiber paper A manufactured by the method shown below was obtained.
[Method for producing carbon fiber paper A]
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.) 25 Mass parts were uniformly dispersed, and paper making was performed using a standard square sheet machine (manufactured by Kumagai Riki Kogyo Co., Ltd.). The obtained paper body was dried with a roll dryer heated to 80 ° C. to obtain a carbon fiber paper A having a mass per unit area of 28 g / m ² .

  Next, the apparent viscosity of a novolac type phenol resin N (trade name: Resitop XPL-6111B, manufactured by Gunei Chemical Industry Co., Ltd.) having a softening point of 80 ° C. by the ring-and-ball method is 50 to 140 mPa · s. A certain resol type phenolic resin R (trade name: Phenolite J-325, manufactured by DIC Corporation) was mixed so that the solid mass ratio was N: R = 80: 20 to obtain a resin composition. Furthermore, it diluted with methanol so that solid content might be 8 mass%, the methanol solution was impregnated in the said carbon fiber paper A, methanol was fully dried at room temperature, 99 mass parts with respect to 100 mass parts of carbon fiber paper. A resin-impregnated paper having a resin solid content adhered thereto was obtained.

Two sheets of the resin impregnated paper are stacked and sandwiched between release papers, placed in a batch press machine at 180 ° C. and 10 MPa for 3 minutes, and then the press pressure is released to naturally cool to room temperature to obtain an intermediate substrate. It was.
Subsequently, the porous base material of the present invention was obtained by heating the intermediate base material in a batch carbonization furnace in a nitrogen gas atmosphere at 2000 ° C. for 1 hour for carbonization. The surface observation photograph by the scanning electron microscope of the obtained porous electrode base material is shown in FIG.

  Resin in which 75 parts by mass of resin solid content was attached to 100 parts by mass of carbon fiber paper in the same manner as in Example 1 except that carbon fiber paper B produced by the method shown below was used as carbon fiber paper. Impregnated paper was obtained, and the porous electrode substrate of the present invention was obtained in the same manner as in Example 1.

[Method for producing carbon fiber paper B]
A carbon short in which a polyacrylonitrile (PAN) carbon fiber having an average fiber diameter of 7 μm and an average fiber length of 3 mm and a PAN carbon fiber having an average fiber diameter of 4 μm and an average fiber length of 3 mm are mixed at 70:30 (mass ratio). Fibers are uniformly dispersed in water in a slurry tank of a wet short net continuous paper making machine, fibrillated into single fibers, and when sufficiently dispersed, short fibers of polyvinyl alcohol (PVA) having an average fiber length of 3 mm (trade name) : VBP105-1, manufactured by Kuraray Co., Ltd.) and 1.1 dtex vinylon short fibers (trade name: Unitika Vinylon F, manufactured by Unitika Co., Ltd.) having an average fiber length of 5 mm and 18 parts by mass with respect to 100 parts by mass of carbon short fibers, respectively. It was uniformly dispersed so as to be 32 parts by mass and sent out as a web. The fed web was passed through a short mesh plate, and after drying the dryer, a carbon fiber paper B having a mass per unit area of 20 g / m ² and a length of 100 m was obtained.

  In the same manner as in Example 2 except that the composition of the resin composition was N: R = 85: 15 in terms of solid content, 74 mass parts of resin solid content was attached to 100 mass parts of carbon fiber paper. Resin-impregnated paper was obtained, and the porous electrode substrate of the present invention was obtained in the same manner as in Example 1.

In the same manner as in Example 1, a methanol solution of the resin composition was obtained, and the carbon fiber paper B was uniformly brought into contact with each side of the roller on which the methanol solution was adhered, and then dried by spraying hot air continuously. A resin-impregnated paper having 128 parts by mass of resin solid content attached to 100 parts by mass was obtained. Next, two sheets of the resin-attached carbon fiber paper are bonded so that the surface in contact with the short mesh plate faces outward, and then, for example, disclosed in Japanese Patent No. 3699447, a continuous belt provided with a pair of endless belts. An intermediate base material (thickness: 110 μm, width 30 cm, length 100 m) having a smooth surface was obtained by continuous heating using a thermal heating and pressing apparatus. At this time, the preheating temperature in the preheating zone was 200 ° C., the preheating time was 5 minutes, the temperature in the heating and pressurizing zone was 250 ° C., and the pressurizing pressure was linear pressure 8.0 × 10 ⁴ N / m. . The intermediate substrate was passed between two release papers so as not to stick to the belt.
Then, the porous base material of this invention was obtained by heating the obtained intermediate base material in a batch carbonization furnace in nitrogen gas atmosphere at 2000 degreeC for 1 hour, and carbonizing.

[Comparative Example 1]
Except that the composition of the resin composition was N: R = 0: 100 in terms of solid content mass ratio, 85 mass parts of resin solid content was adhered to 100 mass parts of carbon fiber paper in the same manner as in Example 1. A resin-impregnated paper was obtained, and a porous electrode substrate was obtained in the same manner as in Example 1. The surface observation photograph by the scanning electron microscope of the obtained porous electrode base material is shown in FIG.

[Comparative Example 2]
In the same manner as in Example 1 except that the composition of the resin composition was N: R = 60: 40 in terms of solid content mass ratio, 99 parts by mass of resin solid content was attached to 100 parts by mass of carbon fiber paper. A resin-impregnated paper was obtained, and a porous electrode substrate was obtained in the same manner as in Example 1.

[Comparative Example 3]
In the same manner as in Example 4 except that the composition of the resin composition was N: R = 0: 100 in terms of solid content mass ratio, 73 mass parts of resin solid content was adhered to 100 mass parts of carbon fiber paper. A resin-impregnated paper was obtained, and a porous electrode substrate was obtained in the same manner as in Example 4.

[Comparative Example 4]
In the same manner as in Example 2 except that the composition of the resin composition was N: R = 90: 10 in terms of solid content mass ratio, 75 mass parts of resin solid content was adhered to 100 mass parts of carbon fiber paper. A resin-impregnated paper was obtained, and a porous electrode substrate was obtained in the same manner as in Example 1.

[Comparative Example 5]
Example 2 except that a resol type phenol resin (trade name: Resitop PL-2211, manufactured by Gunei Chemical Industry Co., Ltd.) whose apparent viscosity of a 60 wt% methanol solution is 170 mPa · s was used as the resol type phenol resin. Similarly, a resin-impregnated paper having 72 parts by mass of resin solid content adhered to 100 parts by mass of carbon fiber paper was obtained, and a porous electrode substrate was obtained in the same manner as in Example 2.

Table 1 shows the physical properties of the porous electrode substrate.

The porous electrode base materials of Examples 1 to 4 each have a specific resistance in the thickness direction as low as 0.72 Ω · cm or less and P> 1. Therefore, it can be said that both the gas permeability and the conductivity in the thickness direction are improved by changing the impregnating resin from a single resol type phenol resin to a resin composition in which a novolac type phenol resin and a resol type phenol resin are mixed.
The porous electrode substrate obtained by the present invention has few cracks in the resin carbonized product and few peeling interfaces with the short carbon fibers, and the water repellent agent is water repellent even if the water repellent treatment essential for the operation of the polymer electrolyte fuel cell is performed. Is unlikely to penetrate and deposit on cracks and debonding sites and hinder the conduction path. Therefore, compared with the case where a water repellent treatment is performed on a base material having many cracks / peeling sites, a decrease in conductivity can be minimized.

The porous electrode substrate obtained in Example 1 was cut into a 5 cm square, and water-repellent treatment [commercially available PTFE dispersion (trade name: 31-JR, manufactured by Mitsui / DuPont Fluorochemical Co., Ltd.) with water up to 20% by weight. It was immersed in the diluted one, dried and sintered at 360 ° C.]. The surface observation photograph by the scanning electron microscope of the obtained porous electrode base material is shown in FIG.
The thickness direction of the specific resistance R ₂ measured for the porous electrode substrate after the water repellent treatment, a difference is that the resistivity of the resistivity R ₁ value before water repellent treatment (identical to the value shown in Table 1) The increase amount ΔR [Ω · cm] and the specific resistance increase rate S [%] were calculated by the following equations.
Increase in specific resistance: ΔR = R ₂ −R ₁
Specific resistance increase rate: S = ΔR / R ₁ × 100

[Comparative Example 6]
ΔR and S were calculated in the same manner as in Example 5 except that the porous electrode substrate obtained in Comparative Example 1 was used.

[Comparative Example 7]
ΔR and S were calculated in the same manner as in Example 5 except that the porous electrode substrate obtained in Comparative Example 2 was used.

The results are shown in Table 2.

  ΔR and S of Example 5 are significantly smaller than those of the comparative example, and satisfy the relationship of ΔR ≦ 0.1 and S ≦ 25.

  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.

Claims (3)

An aggregate of short carbon fibers dispersed in a plane has a novolac type phenol resin N having a softening point of 75 to 95 ° C. measured by the ring and ball method and an apparent viscosity of 50 to 140 mPa · s measured by a B type viscometer. A resin composition obtained by mixing a 60 wt% methanol solution of a resol type phenolic resin R in a solid content mass ratio of N: R = 80: 20 to 85:15 is 100 parts by mass of carbon fiber. Impregnating to 70 to 130 parts by mass to obtain an intermediate substrate;
Heating the intermediate substrate to carbonize the resin composition;
The manufacturing method of the porous electrode base material which has this. A step of immersing the porous electrode substrate obtained by the production method according to claim 1 in a polytetrafluoroethylene dispersion having a solid content of 5 to 30% by weight;
Further drying and sintering polytetrafluoroethylene to the porous electrode substrate;
The manufacturing method of the porous electrode base material which has this. The specific resistance increase ΔR [Ω · cm] and the specific resistance increase rate S [%] in the thickness direction after the water repellent treatment before the water repellent treatment satisfy the relationship of ΔR ≦ 0.1 and S ≦ 25. Item 3. A porous electrode substrate produced by the production method according to Item 2.