JP4730888B2 - Porous electrode substrate and method for producing the same - Google Patents

Description

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

The porous electrode base material is a member located between the separator and the catalyst layer in the polymer electrolyte fuel cell. This material not only functions as an electrical conductor between the separator and the catalyst layer, but also distributes gas such as hydrogen and oxygen supplied from the separator to the catalyst layer and absorbs water generated in the catalyst layer to the outside. It is required to have the function of discharging. At present, carbon is generally considered effective.
Conventionally, in order to increase the mechanical strength, methods such as tightly bonding short carbon fibers and resin carbide were taken, but the gas permeability decreased and the performance when assembled in a fuel cell was reduced. I often fell. On the other hand, if the gas permeability is kept large, the mechanical strength becomes weak and the handling method is limited.

Patent Document 1 describes a porous electrode base material in which pores are formed by using organic fibers and using the disappearance of organic fibers due to carbonization of the electrode base material. However, although the pores formed in this way have a high porosity, the average diameter is small, and the gas permeability is too low for use in a polymer electrolyte fuel cell. In addition, there is a problem that the thickness is large, the size is large, and the cost is high.
Patent Document 2 describes an inexpensive method for producing a porous electrode substrate. Since the porous electrode substrate obtained by this method is oriented in the thickness direction, the thickness direction conductivity and gas permeability are satisfactory values, but the mechanical strength is weak and the thickness direction is low. There were problems in terms of handling, such as oriented fibers breaking through the electrolyte membrane and becoming brittle once pressed.
Patent Document 3 discloses a porous electrode substrate having a pore volume of 0.05 to 0.16 cc / g having a pore diameter of 10 μm or less in order to prevent cracking of the porous carbon substrate and increase mechanical strength. Are listed. However, it is considered that when there are few pores of 10 μm or less as described above, water management is difficult because water retention is small, and power generation of the fuel cell cannot be performed sufficiently.

Japanese Patent Laid-Open No. 9-278558 WO 2001/04980 (Special Table 2003-504822) WO2004 / 085728

  The present invention overcomes the above-mentioned problems and is inexpensive, compact, and suitable for assembling a cell stack. A porous electrode substrate for a polymer electrolyte fuel cell and a method for producing the porous electrode substrate The purpose is to provide.

  The first gist of the present invention is that carbon short fibers having a fiber diameter of 3 to 9 μm dispersed in a random direction in a substantially two-dimensional plane are bound together with an amorphous resin carbide, and further the carbon short fibers The porous electrode base material has a thickness of 150 μm or less, which are cross-linked with filamentous resin carbide.

In addition, the second gist of the present invention is that carbon fiber paper having a fiber diameter of 16 to 40 g / m ² and comprising carbon short fibers having a fiber diameter of 3 to 9 μm and vinylon fibers is impregnated with resin, and then carbonized. A method for producing a porous electrode substrate.
The third gist of the present invention is that a carbon fiber paper having a carbon fiber basis weight of 8 to 20 g / m ² composed of a short carbon fiber having a fiber diameter of 3 to 9 μm and a vinylon fiber is impregnated with a resin and pasted two It is in the manufacturing method of the porous electrode base material which carbonizes after combining.

  According to the present invention, it is possible to obtain a porous electrode base material having a satisfactory gas permeability and an excellent bending strength while being thin and inexpensive. Moreover, according to the manufacturing method of the porous electrode base material of this invention, the said porous electrode base material can be produced at low cost.

<Short carbon fiber>
The carbon fiber that is a raw material of the short carbon fiber used in the present invention may be any of polyacrylonitrile-based carbon fiber, pitch-based carbon fiber, rayon-based carbon fiber, etc., but polyacrylonitrile-based carbon fiber is preferable, and carbon fiber used in particular Is preferably composed only of polyacrylonitrile (PAN) -based carbon fibers since the mechanical strength of the porous carbon electrode substrate can be made relatively high.
The diameter of the short carbon fiber is 3 to 9 μm, which is necessary in terms of production cost, dispersibility, and smoothness of the final porous electrode base material, and is 4 μm or more and 8 μm or less. preferable.
The fiber length of the short carbon fibers is preferably 2 to 12 mm from the viewpoint of binding properties and dispersibility with the binder described below.

<Dispersion>
In the present invention, “substantially dispersed in a random direction within a two-dimensional plane” means that the carbon short fibers lie so as to form a single plane. Thereby, the short circuit by carbon short fiber and the breakage of carbon short fiber can be prevented.

<Resin carbide>
In the present invention, the resin carbide is a substance that binds short carbon fibers and is formed by carbonizing a resin. The resin is preferably a resin having a strong binding force with carbon fibers such as a phenol resin and a large residual weight during carbonization, but is not particularly limited.
Depending on the type of resin and the amount of impregnation into the carbon fiber paper, the ratio of the resin carbide remaining as a carbide on the porous electrode base material varies.
When the porous electrode substrate is taken as 100% by mass, the resin carbide is preferably 25 to 40% by mass, and more preferable lower and upper limits are 28% by mass and 34% by mass, respectively.
In order to bind carbon short fibers completely and keep the mechanical strength of the porous electrode base material at a sufficient level, 25% by mass or more of resin carbide is required. The short carbon fibers that have not been completely bound may fall off the porous electrode base material and pierce the electrolyte membrane, causing a short circuit. On the other hand, it is advantageous to keep the ratio of short carbon fibers in the porous electrode base material high and to make the pores not more than 40% by mass so that the pores are not filled with the resin due to pressurization when the resin is cured.

<Amorphous resin carbide>
In the present invention, first, it is necessary that short carbon fibers are bound together with an amorphous resin carbide, as in a conventional porous electrode substrate.

<Filamentary resin carbide>
In the present invention, from the viewpoint of achieving both mechanical strength and reaction gas / moisture management together with the amorphous resin carbide, the presence of filamentous resin carbide that crosslinks the short carbon fiber and the short carbon fiber is necessary.
This filamentous resin carbide has a different appearance from short carbon fibers, and the orientation of the carbon constituting the filamentous resin carbide is very well oriented in the arrangement of carbon in the short carbon fibers. On the other hand, it is the same as the above-mentioned amorphous resin carbide.
FIGS. 1 and 2 show a state in which short carbon fibers and short carbon fibers are crosslinked with filamentous resin carbide. The filament-shaped resin carbide provides a porous electrode base material with high mechanical strength even when the thickness is small. The reason for this is that the filamentous resin carbide performs the same reinforcing effect as the carbon short fibers, so that the ratio of the carbon short fibers contained in the porous electrode substrate can be reduced and provided at low cost. it can.
At the same time, since the filamentous resin carbide has some large pores divided by crosslinking, the porous electrode substrate of the present invention has wide pores having a radius of 5 μm or less and a pore of 25 μm or more. It has a pore size distribution. As a result, the porous electrode substrate of the present invention has both a function of smoothly discharging reaction gas and generated water from the porous electrode substrate and a water retention property that prevents the electrolyte membrane from drying and reducing the efficiency of the reaction. This is because the former function is performed by large pores of 25 μm or more, and the latter function is performed by relatively small pores of 5 μm or less. Thus, when the distribution range of the pore diameter is wide, it is advantageous to satisfy both functions required for the porous electrode substrate.

<Thickness>
The porous electrode substrate of the present invention is required to have a thickness of 150 μm or less, preferably 140 μm or less, and more preferably 130 μm or less. Although a porous electrode substrate having a thickness of more than 150 μm has been used, it is not preferable for cost reduction and compactness of the cell stack in the future. The electrical resistance in the penetration direction can also be reduced as the thickness is reduced.
A porous electrode substrate having a smaller thickness is more likely to maintain the flow rate of the reaction gas and stabilizes the performance of the entire cell.

<Bending fracture load>
A feature of the present invention is that it has a sufficient bending fracture load as described below, despite being such a thin porous electrode substrate. The porous electrode substrate of the present invention has a bending breaking load of 0.06 N or more in at least one direction even when the thickness is 150 μm or less. More preferably, even when the thickness is 130 μm or less, a mechanical strength with a bending breaking load of 0.06 N or more is exhibited in at least one direction. More preferably, it has a bending fracture load of 0.11 N or more in at least one direction.
The bending fracture load in the present invention is a value obtained by a method based on JIS standard K-6911, and represents the strength against bending fracture. The value of the bending rupture load varies depending on the strain rate, the distance between the fulcrums, and the width of the test piece. Use breaking load.
In order to prevent problems such as cracking and tearing in the handling of products in the continuous manufacturing process of porous electrode base materials or the manufacturing process of MEA (membrane-electrode assembly) using this porous electrode base material It is preferable that the bending fracture load in the one direction is 0.06 N or more.
In conventional porous electrode base materials, if the thickness is reduced, the generated gas cannot be discharged or becomes brittle, which often impedes handling in the above process.
As a method for improving the mechanical strength while maintaining satisfactory gas permeability of the porous electrode base material, there is a method of increasing the fiber length of the short carbon fiber, but uniform dispersibility may be a problem. was there.

<Unit weight>
The porous electrode base material of the present invention needs to have a carbon fiber basis weight (weight per unit area) of 16 to 40 g / m ² . At this time, it is most preferable to stack two carbon fiber papers having a half basis weight to obtain the above basis weight. The short carbon fiber is not only a conductive material but also serves as a reinforcing material for the porous electrode substrate.
By setting the basis weight of the carbon fiber to 16 g / m ² or more, the strength of the porous electrode substrate can be made sufficient. In addition, when the thickness is 40 g / m ² or less, an excessively dense structure is not obtained even if the thickness is 150 μm or less.
Moreover, the porous electrode base material of the present invention can be continuously wound, which is preferable from the viewpoints of productivity and cost of porous electrode materials and fuel cells. In particular, the porous electrode base material of the present invention is easy to handle because the thickness can be reduced, so that it is preferably wound continuously.

<Pore radius distribution>
The porous electrode substrate of the present invention has a volume per unit weight of 0.20 to 1.00 cc / g when the pore distribution is measured by mercury porosimetry and the radius of the pore is 5 μm or less. It is preferable. Further, the pore volume of pores having a pore radius of 10 μm or less is preferably 15% or more, more preferably 20% or more of the total pore volume.
The porous electrode substrate for fuel cells not only has a function of efficiently delivering the reaction gas to the reaction part (catalyst layer), but also has a function of efficiently discharging moisture contained in the reaction gas and moisture generated by power generation. It has been demanded. In particular, in order to efficiently discharge water in a thin electrode substrate, the unit weight of pores having a radius of 5 μm or less as pores for temporarily taking in water when a large amount of moisture is generated It is preferable that the permeation volume is 0.20 cc / g or more, or the pore volume of 10 μm or less is 20% or more of the total pore volume. When carbon short fibers are reinforced by cross-linking with filamentous resin carbide, small pores are formed, and the volume per unit weight of pores having a radius of pores of 5 μm or less is 0.20 cc / g. As described above, the pore volume having a pore radius of 10 μm or less can have 15% or more of the total pore volume. Alternatively, when the volume per unit weight of the pores having a pore radius of 5 μm or less is larger than 1.00 cc / g, it is not preferable because moisture is hardly discharged to the outside. The pore radius and pore volume are calculated from the pressure in the measurement cell and the mercury volume injected at that time.

<Winding form>
The porous electrode base material of the present invention is preferably wound around a paper tube having a diameter of 3 inches or less from the viewpoint that the equipment used for manufacturing and the packaged product can be made compact. When the paper tube size is small, it is preferable also in that it is easy to carry.

<Manufacturing method>
The method for producing the porous electrode substrate of the present invention is, for example, according to the following method. That is,
A method for producing a porous electrode substrate that is carbonized after impregnating a resin into carbon fiber paper having a carbon fiber basis weight of 16 to 40 g / m ² , comprising carbon short fibers having a fiber diameter of 3 to 9 μm and vinylon fibers, or A porous electrode made of carbon short fibers and vinylon fibers having a fiber diameter of 3 to 9 μm, impregnated with carbon fiber paper with a carbon fiber basis weight of 8 to 20 g / m ² , and bonded together, and then carbonized. It is a manufacturing method of a base material.

<Vinylon fiber>
In the production method of the present invention, it is necessary to use vinylon fibers. The vinylon fiber is a fiber having improved heat resistance and water resistance by acetalizing polyvinyl alcohol fiber with heat treatment or formaldehyde. The vinylon fiber is not decomposed by carbonization, but the shape of the resin adhered around it remains as it is, and the resin forms filamentary carbide.
The fineness of the vinylon fiber is not particularly limited, but is preferably 0.05 to 1.5 dtex. By setting the fineness to 0.05 dtex or more, the resin per vinylon fiber can be sufficiently adhered, and after carbonization, the filamentous resin carbide can be prevented from peeling off from the porous electrode substrate. By setting the fineness to 1.5 dtex or less, the surface of the porous electrode substrate can be prevented from becoming rough, and when the fuel cell is formed, the contact between the porous electrode substrate and the peripheral member can be improved. .
The length of the vinylon fiber is not particularly limited, but is preferably the same as the short carbon fiber used at the same time. From the viewpoint of binding properties and dispersibility with the binder, 2 to 12 mm is preferable.
The vinylon fiber also serves to prevent the carbon fiber from refocusing by being dispersed together with the carbon fiber. Therefore, what is excellent also in the affinity with water is preferable.
The mass ratio of vinylon fibers in the carbon fiber paper is preferably 10 to 60% by mass.
By making the mass ratio of the vinylon fiber in the carbon fiber paper 10% by mass or more, the reinforcing effect by the filamentous carbide derived from the vinylon fiber is sufficient. On the other hand, if the mass ratio is 60% by mass or less, the filamentous carbide and the other The balance of carbides is good, and the form of the porous electrode substrate can be satisfactory.

<Organic polymer compound>
The organic polymer compound serves as a binder (glue) that holds the components together in the carbon fiber paper. As the organic polymer compound, polyvinyl alcohol (PVA), polyvinyl acetate, or the like can be used. In particular, polyvinyl alcohol is preferable as a binder because it has excellent binding power in the paper making process, and the short carbon fibers are not dropped off. In the present invention, it is also possible to use an organic polymer compound as a fiber.

<Carbon fiber paper making>
As a paper making method for carbon fiber paper, a wet method in which short carbon fibers are dispersed in a liquid medium for paper making or a dry method in which carbon short fibers are dispersed in air to be deposited can be applied. Is preferred. In order to help disperse the short carbon fibers into single fibers and prevent the dispersed single fibers from converging again, it is possible to wet-paper the vinylon fibers with the above-mentioned amount and an appropriate amount of organic polymer substance as a binder. preferable.
There are two methods for mixing short carbon fibers and vinylon fibers and, if necessary, organic polymer compounds with stirring and dispersing in water together with short carbon fibers and direct mixing. The method of diffusing and dispersing with is preferable. By mixing the organic polymer compound in this way, the strength of the carbon fiber paper is maintained, and it is possible to prevent the carbon short fibers from being peeled off from the carbon fiber paper during the production and the orientation of the carbon short fibers from being changed. can do.
Further, there are a continuous paper making method and a batch paper making method. However, the paper making performed in the present invention is preferably continuous paper making from the viewpoint of easy control of the basis weight and productivity and mechanical strength.

<Resin>
The resin composition used as a resin in the present invention is a substance that remains as a conductive substance even after carbonization, and preferably exhibits adhesiveness or fluidity at room temperature. A phenol resin, a furan resin, an epoxy resin, a melamine resin, an imide resin, a urethane resin, an aramid resin, pitch, or the like can be used alone or as a mixture. Preferable examples of the phenol resin include a resol type phenol resin obtained by a reaction between a phenol and an aldehyde in the presence of an alkali catalyst.
The resol type phenol resin can be dissolved and mixed with a novolac type phenol resin which is produced by the reaction of phenols and aldehydes in the presence of an acid catalyst by a known method and exhibits solid heat-fusibility. Is preferably a self-crosslinking type containing a curing agent such as hexamethylenediamine.
As phenols, for example, phenol, resorcin, cresol, xylol and the like are used. As aldehydes, for example, formalin, paraformaldehyde, furfural and the like are used. Moreover, these can be used as a mixture. These can also use a commercial item as a phenol resin.

<Resin amount>
The amount of resin adhering to the carbon fiber paper is preferably 70 to 150 parts by mass with respect to 100 parts by mass of the carbon short fibers. In order to produce an electrode base material that is smoothly supplied and discharged and has excellent bending strength as described above, the ratio of the resin carbide in the porous electrode base material is 25 to 40% by mass. Since it is necessary to adhere the resin to 70 to 150 parts by mass of resin, it is necessary to adhere the resin.

<Resin impregnation method>
The carbon fiber paper is impregnated with the resin as long as the carbon fiber paper can be impregnated with the resin, and there is no particular limitation. However, a method of uniformly coating the resin on the surface of the carbon fiber paper using a coater, The dip-nip method using the apparatus, or the method of transferring the resin to the carbon fiber paper by stacking the carbon fiber paper and the resin film can be performed continuously, and the productivity and the length can be manufactured. preferable.

<Curing and carbonization of resin>
The carbon fiber paper impregnated with the resin can be carbonized as it is. However, curing the resin before carbonization is preferable for suppressing the vaporization of the resin during carbonization and improving the strength of the porous electrode substrate. Any technique can be applied for the curing as long as the technique can uniformly heat the carbon fiber paper impregnated with the resin. Examples thereof include a method in which rigid plates are stacked from both the upper and lower surfaces of carbon fiber paper impregnated with resin and heated, a method in which hot air is blown from both the upper and lower surfaces, and a method using a continuous belt device and a continuous hot air furnace.
The cured resin is subsequently carbonized. In order to increase the conductivity of the porous electrode substrate, it is carbonized in an inert gas. Carbonization is preferably performed continuously over the entire length of the carbon fiber paper. If the electrode base material is long, not only the productivity of the electrode base material is increased, but also the subsequent process of manufacturing the membrane electrode assembly (MEA) can be performed continuously, which greatly contributes to the cost reduction of the fuel cell. can do.
Carbonization is preferably performed by continuous firing over the entire length of the carbon fiber paper in a temperature range of 1000 to 3000 ° C. in an inert treatment atmosphere. In the carbonization of the present invention, a pretreatment by firing in an inert atmosphere of about 300 to 800 ° C., which is performed before a carbonization treatment in a temperature range of 1000 to 3000 ° C. in an inert atmosphere, is performed. You can go.
It is preferable to include a step of smoothing the surface of the carbon fiber paper by heating after attaching the resin to the carbon fiber paper. The method of smoothing the carbon fiber surface is not particularly limited, and there are a method of performing hot pressing with smooth rigid plates from both the upper and lower surfaces and a method of using a continuous belt press apparatus. Among these, the method performed using a continuous belt press is preferable in that a long porous electrode substrate can be formed. If the porous electrode base material is long, not only the productivity of the porous electrode base material is increased, but the subsequent MEMBRANE ELECTRODE ASSEMBLY (MEA) manufacturing can also be continuously performed, thereby reducing the cost of the fuel cell. Can greatly contribute. Even if there is no step to smooth the surface, a porous electrode substrate having both good strength and gas permeability can be obtained, but since the porous electrode substrate has large undulations, it is porous when the cells are assembled. The contact between the porous electrode substrate and the peripheral substrate is not preferable because it is not sufficient.
As a pressing method in the continuous belt device, there are a method of applying pressure to the belt by a roll press by a linear pressure and a method of pressing by a surface pressure by a hydraulic head press, but the latter is a smoother porous electrode substrate. It is preferable in that it is obtained. In order to effectively smooth the surface, it is best to press at a temperature at which the resin is most softened, and then fix the resin by heating or cooling. When the ratio of the resin impregnated in the carbon fiber paper is large, it is easy to make it smooth even if the press pressure is low. In this case, it is not preferable to increase the pressing pressure more than necessary because problems such as excessively dense structure and severe deformation occur when the porous electrode substrate is used. If the press pressure is too high and too dense, the gas generated during firing may not be discharged well and the structure of the porous electrode substrate may be destroyed. When curing the resin impregnated in carbon fiber paper with a rigid belt device with a continuous belt device, either apply a release agent in advance to prevent the resin from adhering to the rigid plate or belt, It is preferable that the release paper is sandwiched between a rigid plate and a belt.

Hereinafter, the present invention will be described more specifically with reference to examples.
Each physical property value in the examples was measured by the following method.

1) Bending fracture load Ten sheets are cut into a size of 80 × 10 mm so that the longitudinal direction of the carbon fiber paper in the porous electrode base material is the long side of the test piece. Using a bending strength test apparatus, the distance between supporting points was set to 2 cm, a load was applied at a strain rate of 10 mm / min, and the load when the test piece broke was measured. It is an average value of 10 test pieces.

2) Gas permeability It is calculated | required by the method based on JIS specification P-8117. A porous electrode substrate test piece is sandwiched between cells having a 3 mmφ hole, 200 mL of gas is allowed to flow from the hole at a pressure of 1.29 kPa, and the time taken for the gas to permeate is measured. Calculated.
Gas permeability (m / sec · MPa)
= Gas permeation amount (m ³ ) / gas permeation hole area (m 2) / permeation time (sec) / permeation pressure (MPa)

3) Average pore radius of electrode substrate, total pore volume, volume of pores with a radius of 10 μm or less, volume of pores with a radius of 5 μm or less Using the mercury intrusion method, the pore distribution of pore volume and pore radius The radius at which the 50% pore volume was obtained was taken as the average pore diameter of the electrode substrate. The mercury porosimeter used was Pore Master-60 manufactured by Quantachrome.

4) Thickness The thickness of the porous electrode base material was measured using a thickness measuring device dial thickness gauge 7321 (manufactured by Mitutoyo Corporation). The size of the probe at this time was 10 mm in diameter and the measurement pressure was 1.5 kPa.

5) Sheet resistance Cut out to a size of 100 × 20 mm so that the longitudinal direction of the carbon fiber paper in the porous electrode substrate during papermaking becomes the long side of the test piece. A copper wire was placed on one side of the electrode substrate with an interval of 2 cm, and the resistance when a current was passed at a current density of 10 mA / cm ² was measured.

6) Through-direction resistance The electrical resistance in the thickness direction of the porous electrode base material (through-direction resistance) is obtained by sandwiching a sample between copper plates, pressurizing at 1 MPa from the top and bottom of the copper plate, and passing a current at a current density of 10 mA / cm ^2. The resistance value was measured and obtained from the following equation.
Penetration resistance (Ω · cm ² ) = Measurement resistance value (Ω) × Sample area (cm ² )

7) Weight ratio of resin carbide The weight ratio of the resin carbide was calculated from the following formula from the basis weight of the obtained porous electrode substrate and the basis weight of the carbon short fibers used.
Resin carbide weight ratio (mass%)
= [Porous electrode substrate basis weight (g / m ² ) −carbon short fiber basis weight (g / m ² )] × 100 ÷ Porous electrode substrate basis weight (g / m ² )

Example 1
As short carbon fibers, 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 70:30 (mass ratio). The carbon short fiber mixed with was prepared.
As a vinylon fiber, 1.1 dtex and a vinylon short fiber having a cut length of 5 mm (Unitika Vinylon F manufactured by Unitika Ltd.) were prepared.
As an organic polymer compound, a short fiber of polyvinyl alcohol (PVA) (V PB 105-1 manufactured by Kuraray Co., Ltd., cut length: 3 mm) was prepared.
Carbon short fibers are uniformly dispersed in water in a slurry tank of a wet short net continuous paper making machine to be defibrated into single fibers, and when sufficiently dispersed, PVA short fibers and vinylon short fibers are added to 100 parts by mass of carbon short fibers. Then, they were uniformly dispersed so as to be 18 parts by mass and 32 parts by mass, respectively, and fed into a web shape.
The fed web was passed through a short mesh plate, and after drying with a dryer, carbon fiber paper having a basis weight of 20 g / m ² and a length of 100 m was obtained (the basis weight of each composition is described in Table 1, the same applies hereinafter). The dispersion state of each fiber was good.
Next, carbon fiber paper was uniformly contacted one side at a time on a roller to which a phenol resin methanol solution containing 40% by mass of phenol resin (Phenolite J-325 manufactured by Dainippon Ink and Chemicals, Inc.) was attached, and then hot air continuously. And dried. A resin-attached carbon fiber paper of 32 g / m ² was obtained. As a result, 90 parts by mass of the phenol resin was attached to 100 parts by mass of the short carbon fibers.
Next, two sheets of this resin-attached carbon fiber paper were bonded so that the surface in contact with the short mesh plate faced outward, and then a continuous heating press device (double belt press device: DBP) provided with a pair of endless belts. ) To obtain a sheet having a smooth surface (sheet thickness: 110 μm, width 30 cm, length 100 m).
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 pressing zone was 250 ° C., and the press pressure was 8.0 × 104 N / m. The sheet was passed between two release papers so as not to stick to the belt.
Thereafter, the obtained sheet was heated in a continuous baking furnace at 500 ° C. in a nitrogen gas atmosphere for 5 minutes to cure and pre-carbonize the phenol resin. Subsequently, the obtained sheet was heated in a continuous firing furnace at 2000 ° C. for 5 minutes in a nitrogen gas atmosphere and carbonized to continuously obtain an electrode substrate having a length of 100 m, and formed into a cylindrical paper tube having an outer diameter of 3 inches. Winded up.
Although it was thinned, it was an electrode substrate that was smooth, easy to handle, and excellent in bending strength and gas permeability. The evaluation results are shown in Tables 2 and 3. Further, the SEM photograph is shown in FIG. 1 and FIG. 2 shows the pore distribution in FIG. Since there is a portion where the resin carbide is not crosslinked, the pore distribution range is widened, and the pore volume of pores having a pore radius of 10 μm or less accounts for 30% of the total pore volume.

(Example 2)
A porous electrode substrate having a smooth surface was obtained in the same manner as in Example 1 except that the ratio of short carbon fibers was changed to 50/50 (mass ratio). The evaluation results are shown in Tables 2 and 3.

(Example 3)
A porous electrode substrate having a smooth surface was obtained in the same manner as in Example 1 except that the vinylon fiber was replaced with 0.6 dtex and a vinylon short fiber having a cut length of 5 mm (Unitika Vinylon F manufactured by Unitika Ltd.). The evaluation results are shown in Tables 2 and 3.

Example 4
A porous electrode substrate having a smooth surface was obtained in the same manner as in Example 3 except that the addition amount was changed so that the basis weight of the vinylon fiber was 10 g / m ² . The evaluation results are shown in Tables 2 and 3.

(Example 5)
A porous electrode substrate having a smooth surface was obtained in the same manner as in Example 1 except that only PAN-based carbon fibers having an average fiber diameter of 4 μm and an average fiber length of 3 mm were used as the short carbon fibers. The evaluation results are shown in Tables 2 and 3.

(Comparative Example 1)
A carbon fiber paper of 15 g / m ² was used in the same manner as in Example 1 except that only a PAN-based carbon fiber having an average fiber diameter of 7 μm and an average fiber length of 3 mm was used as the short carbon fiber, and no vinylon fiber was added. Obtained. In the same manner as in Example 1, 100 parts by mass of phenol resin was attached to 100 parts by mass of carbon fiber short fibers on this carbon fiber paper to obtain 28 g / m ² of resin-attached carbon fiber paper.
Thereafter, an attempt was made to obtain a porous electrode substrate by the same method as in Example 1. However, under the same conditions as in Example 1, since innumerable wrinkles entered after heating and pressurization, when the preheating temperature was raised from 200 ° C. to 230 ° C., the wrinkles disappeared, so this condition was adopted. Was fired in the same manner as above to obtain a porous electrode substrate. The obtained porous electrode substrate was brittle and difficult to handle. The evaluation results are shown in Tables 2 and 3. Also shows the pore distribution of the porous electrode substrate in FIG. Since the peak was sharp and the pore volume of pores of 10 μm or less was only 19% of the total pore volume, it was difficult to manage the generated water, and it was expected that the performance was low even when incorporated in a cell.

(Comparative Example 2)
An electrode substrate was obtained in the same manner as in Comparative Example 1 except that the basis weight of the carbon fiber paper was 30 g / m ² and the basis weight of the resin-attached carbon fiber paper was 56 g / m ² . The porous electrode substrate became stronger as the basis weight increased, but it was brittle and difficult to handle. The evaluation results are shown in Tables 2 and 3.

  The present invention provides an electrode base material for a polymer electrolyte fuel cell that is suitable for overcoming the problems of the prior art, is inexpensive and compact, and forms a cell stack, and a method for producing the electrode base material.

It is an electron micrograph of the porous electrode base material surface of this invention. It is an electron micrograph of the porous electrode base material surface of this invention. The magnification is higher than in FIG. It is the graph which showed the pore diameter distribution of the porous electrode base material of this invention.

Claims (1)

Carbon short fibers having a fiber diameter of 3 to 9 μm and a fiber length of 2 to 12 mm dispersed in a random direction in a substantially two-dimensional plane are bound together with an amorphous resin carbide, and the carbon short fibers are filaments. A porous electrode base material having a thickness of 150 μm or less, which is crosslinked by a resin carbide in a shape,
When the pore distribution was measured by mercury porosimetry of the porous electrode substrate, the volume per unit weight of the pores having a radius of 5 μm or less was 0.20 to 1.00 cc / g, and the radius was A porous electrode substrate , wherein the pore volume of pores of 10 μm or less is 15% or more of the total pore volume .

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