JPH067489B2 - Flexible water-repellent firing carbon substrate and its manufacturing method, fuel cell electrode and fuel cell - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a water-repellent fired carbon substrate having flexibility, a method for producing the same, a fuel cell electrode using the carbon substrate, and a fuel cell.

The carbon substrate of the present invention is suitable for use as an electrode substrate of a methanol fuel cell, and particularly preferably for use as a laminated base formed by laminating a plurality of unit cells.

[Background of the Invention]

In a methanol fuel cell or fuel storage using phosphoric acid as an electrolyte and hydrogen as a fuel, the electrode is usually composed of a porous conductive substrate and a catalyst layer. A carbon substrate is often used as the porous conductive substrate, and in particular, carbon paper is often used in the methanol fuel cell.
An example of this type of fuel cell electrode is described in JP-A-56-96458.

This publication describes forming a catalyst layer composed of a uniform mixture of catalytic carbon particles and a water-repellent binder on the surface of a conductive carbon cloth having open pores to form a fuel cell electrode. There is. It is described that the conductive carbon cloth having open pores is made by carbonizing a pre-fired carbonaceous fabric at a high temperature, and the catalytic carbon particles include catalytic metal particles deposited on the carbon support particles.

According to the study by the present inventors, carbonized carbonaceous fabrics are very brittle. For example, carbon paper consisting of carbon fibers and an organic binder easily breaks and divides when bent. The brittleness of carbon paper is also described in the above publication. See, for example, page 4, lower left column, lines 5-10.

There are many problems when assembling a fuel cell having a laminated structure by forming electrodes using such a brittle carbon substrate. For example, the carbon substrate is broken when the cells are stacked and tightened. When the carbon substrate is broken, fuel leakage or oxidant leakage occurs. Further, there are many problems when the fuel cell is used as a mobile power source, and the carbon substrate is damaged during repeated use, resulting in fuel leakage or oxidant leakage.

The methanol fuel cell is suitable for a small mobile power source because of safety of fuel and low battery voltage, and is promising as a mobile power source for household electric appliances and a power source for leisure electric appliances, for example. Therefore, compared with the stationary type such as a fuel cell for electric power, it is required to have durability against diversification of cell shape and vibration as a product. It is inappropriate to use a brittle carbon substrate in such a methanol fuel cell for a mobile power source.

[Object of the Invention]

An object of the present invention is to provide a flexible combustion substrate using carbon paper.

Another object of the present invention is to provide a method for manufacturing a flexible fired substrate using carbon paper.

Yet another object of the present invention is to provide an electrode for a fuel cell having a water-repellent fired substrate made of carbon paper and having flexibility as a conductive substrate, and a fuel electrode using such an electrode.

[Outline of Invention]

The fired substrate of the present invention comprises a carbon paper in which voids are impregnated with polytetrafluoroethylene, and the carbon fibers constituting the carbon paper are finely cut, and the polytetrafluoroethylene is cut at one or more locations of the cut portion. Is impregnated.

The present invention is based on the discovery that commercially available carbon paper is coated with polytetrafluoroethylene, fired, and then rolled to have flexibility.

Commercially available carbon paper is composed of carbon fiber and binder, and is carbonized by firing at a high temperature of 2000 ° C or higher. Carbon paper with various thicknesses is commercially available, and 0.1 to 1 mm for methanol fuel cells.
The thickness of is suitable. An organic binder such as a phenol resin is used as a binder for commercially available carbon paper, and this binder is also carbonized by firing at high temperature. That is, in commercially available calcined carbon paper, the binder has no or almost no function as a binder.

As described above, the carbonized carbon paper is easily broken by simply bending it into an arc shape.

When carbon paper is used as a substrate for a fuel cell electrode, it is often used after being made water repellent. The water repellent treatment is
For example, it is carried out by impregnating carbon paper with polytetrafluoroethylene suspension.

The present inventors succeeded in imparting flexibility by firing and rolling carbon paper thus treated with polytetrafluoroethylene, and provided flexibility and water repellency. We succeeded in obtaining a fired carbon substrate. Further, it has been found that flexibility can be imparted by firing after rolling. However, in this case, the deformation of the substrate due to the firing after rolling is very small.

The structure of commercially available carbon paper which had been treated with polytetrafluoroethylene and then calcined and rolled, or calcined and then calcined was found to have the following constitution. That is, the carbon fibers in the carbon paper are finely cut, and substantially all of the voids between the carbon fibers and at least one of the cut portions of the carbon fibers are impregnated with polytetrafluoroethylene.

On the carbon substrate before rolling, almost no cut portions of carbon fibers were seen, and only the voids between the carbon fibers were impregnated with polytetrafluoroelene. In the carbon substrate of the present invention, the carbon fibers are cut by rolling, and part of the polytetrafluoroethylene impregnated in the voids between the carbon fibers is washed away and invaded therein.

In the carbon substrate of the present invention, the number of carbon fiber cut portions is preferably 20 or more per 1 mm ² , and is preferably 30.
It is desirable not to exceed 0. If the number of cut parts of the carbon fiber is small, flexibility is not imparted, and if it is too large, the strength becomes weak and it is not suitable as a substrate for fuel cell electrodes. The number of carbon fiber cut parts of 20 or more per 1 mm ² is much larger than the number of carbon fiber cut parts of ordinary commercially available calcined carbon paper, and can be obtained by applying processing such as rolling or pressing. To be A particularly preferable range of the number of cut portions of carbon fiber is 50 to 150.
It is an individual.

The polytetrafluoroethylene that has penetrated into the cut portion of the carbon fiber serves as a binder for joining the cut carbon fibers. Such a binder action of polytetrafluoroethylene is not found only in the case where commercially available calcined carbon paper is treated with polytetrafluoroethylene. Polytetrafluoroethylene most preferably penetrates into all the carbon fiber cuts,
It is desirable that at least 1/3 of the number of cut portions penetrates.

By treating the carbon paper with polytetrafluoroethylene and then rolling, a gap is formed at a part of the interface between the polytetrafluoroethylene impregnated in the voids between the carbon fibers and the carbon fibers. This gap is rather preferable because it gives flexibility to the carbon substrate.

The final thickness of the carbon substrate according to the present invention is 0.1 to 1 mm.
Is desirable. When the thickness of the carbon substrate becomes thicker, the carbon fibers inside the substrate become difficult to cut,
Flexibility becomes poor. The minimum thickness of the carbon substrate is determined in terms of manufacturing carbon paper, and the present invention can be applied to the minimum thickness that can be manufactured, and flexibility can be imparted.

The method for manufacturing a carbon substrate of the present invention comprises a step of impregnating carbon paper with polytetrafluoroethylene suspension,
Then, it has the process of baking above the melting temperature of polytetrafluoroethylene, and below decomposition temperature, and the process of rolling or pressing. It is desirable to perform rolling or pressing after the firing step. You may reverse. The firing temperature is preferably in the range of 330 to 400 ° C. This firing step is necessary to give polytetrafluoroethylene a function as a binder.

Rolling or pressing can be applied as a means for cutting the carbon fibers. The thickness reduction rate at this time is 60-
80% is desirable.

A fuel cell electrode is obtained by forming a catalyst layer on the carbon substrate of the present invention. The catalyst layer is composed of conductive particles carrying a catalytically active component and a binder. The conductive particles are preferably composed of carbon particles, and acetylene black, furnace black or the like can be used. The catalytically active component is selected from the noble metals selected from Group VIII of the Periodic Table of the Elements, such as platinum, ruthenium, rhodium, palladium, isodium, etc., with platinum being particularly preferred. Any known method can be used for forming the catalyst layer on the carbon substrate. For example, JP-A-56-96458.
The means described in the publication can be applied.

It is desirable to use polytetrafluoroethylene as the binder in the catalyst layer, and after the catalyst layer is formed in order to cause this polytetrafluoroethylene to act as a binder, it is fired at a melting temperature of polytetrafluoroethylene or higher and a decomposition temperature or lower. It is necessary. This firing temperature is also desirably in the range of 330 to 400 ° C.

When a fuel cell is manufactured using polytetrafluoroethylene-treated carbon paper, the rolling or pressing process in manufacturing the carbon substrate can be shifted after the catalyst layer is formed. That is, rolling or pressing may be performed after the catalyst layer is formed and fired. Final thickness of catalyst layer is 0.05
A range of up to 0.5 mm is desirable.

The fuel cell of the present invention has a pair of electrodes, a fuel chamber, and an oxidant chamber that face each other. The anode of the pair of electrodes can be referred to as a fuel electrode, and the cathode can be referred to as an oxidant electrode. In a methanol fuel cell, anolyte containing methanol is introduced into the fuel chamber and air is introduced into the oxidant chamber. An electrolyte is introduced between the pair of electrodes, and this introduction can be performed by using an ion exchange membrane containing the electrolyte.

The methanol fuel cell is used by stacking a plurality of unit cells. At this time, the stacked unit cells are tightened with bolts or the like. The tightening pressure is about 3 with a 40 cell stack.
It can reach Kg / mm ² . The fuel cell using the carbon substrate of the present invention as the electrode substrate does not break due to this tightening pressure.

In a methanol fuel cell, it is desirable to make the pore size and / or pore volume of the cathode catalyst layer different from the pore size and / or pore volume of the catalyst layer of the anode so as to make it larger in the cathode. This makes it possible to further increase the battery voltage. In order to make the pore diameter and / or the pore volume of the catalyst layer different between the anode and the cathode, it is desirable to perform rolling or pressing after the catalyst layer is formed and to change the plate reduction rate at that time. Specifically, for the anode, the plate thickness is 20 to 40% of the thickness before processing.
Processing to make it thin, that is, 60 to 80 of the plate thickness before processing
It is desirable to process so that the plate thickness becomes%. Regarding the cathode, it is desirable that the thickness is not less than 80% of the plate thickness before processing, and preferably the plate thickness reduction is 15 to less than 20% of the plate thickness before processing.

Example of Invention

FIG. 1 shows a sectional view of a single cell (single cell) of a methanol fuel cell according to the present invention as an example. An actual battery has a form in which a large number of these are stacked.

A single cell structure of a methanol fuel cell has a pair of opposed electrodes, that is, an anode 3 and a cathode 8, and an electrolyte-retaining ion exchange membrane 11 sandwiched between these electrodes. The anode 3 comprises a conductive porous substrate 4 and a catalytically active component-supporting conductive porous particle layer 5 formed on at least the surface of the substrate on the electrolyte side. The cathode 8 comprises a conductive porous substrate 9 and a catalytically active component-supporting conductive porous particle layer 10 formed on at least the electrolyte-side surface of the substrate.

The fuel separating plate 1 is provided on the side opposite to the electrolyte side of the anode 3.
The surface of the fuel separation plate (collector plate) 1 in contact with the anode has a plurality of grooves for supplying annolyte containing methanol. A space called a fuel chamber 2 is formed by these grooves and the anode covering the openings of the respective grooves.

Similarly, a gas separating plate (current collecting plate) 6 is provided on the opposite side of the cathode 8 from the electrolyte side, and a plurality of grooves for supplying a gas containing oxygen are provided on the cathode side of the gas separating plate 6. Have. A space called an oxidant chamber 7 is formed by these grooves and the anode covering the openings of the grooves.

The structure shown in FIG. 1 is the same as a very general structure of a single cell of a methanol fuel cell. When stacking such single cells to form a battery, sufficient tightening is performed to minimize the contact resistance between the cells. At that time, the ribs 12 of the separation plates (current collectors) 1 and 6 press the electrodes 3 and 8 together, so that the relatively hard electrode is partially damaged. As a result, the battery performance deteriorates due to the fact that methanol, which is the fuel, goes around to the oxidizer electrode and the electrolyte solution leaks into the oxidizer chamber.

From the above, it is necessary to prevent damage to the electrodes due to tightening of the laminated battery. For that purpose, it is necessary to make the entire electrode flexible.

One way to make the electrodes flexible is to use carbon felt instead of carbon paper as the conductive porous substrate which is the electrode substrate. However, all of the commercially available products of this type have high electric resistance (1 Ω · cm ² or more), and output reduction due to IR loss is large, and it cannot be said to be a practical substrate material.

Therefore, we examined the case where the electrode used conventionally is rolled.

As a result, they have found that applying conventional electrodes to the rollers provides great flexibility. Also, the same result was obtained by pressing.

Since the liquid fuel is used in the anode, a good fuel electrode can be obtained by passing the liquid between the rollers set to 80% or less of the initial electrode thickness several times or more.
This rolling dimension is preferably 60 to 80 of the initial electrode thickness.
%. On the other hand, in the air electrode, since it is a gas diffusion electrode, if the electrode is rolled and thinned, gas diffusion is hindered by the electrolytic solution and the performance deteriorates.
It is desirable to make it above.

Example 1 Commercially available 0.4 mm thick carbon paper was rolled. This commercially available carbon paper is composed of carbon fibers and an organic binder and carbonized by high temperature firing. When the carbon paper before rolling was bent, it cracked and broke at a bending angle of 60 °. The rolled product did not break even when bent at an angle of 60 °, and a cylinder having a diameter of 5 cm could be produced.

The electric resistances of the above-mentioned two carbon papers and commercially available carbon felts were measured in order to see the applicability to electrodes for fuel cells. The electric resistance was measured by sandwiching a carbon paper or carbon felt between two metal plates serving as a current collector and pressing the metal plate.
The relationship between the electric resistance and the pressing pressure is shown in FIG.

Carbon paper has a slightly lower electric resistance due to rolling, and is more suitable as a substrate for fuel storage electrodes.

Example 2 In this example, the conventionally used anode and cathode were rolled to about 70% of the initial electrode thickness, and the flexibility of the electrode, the electrical resistance, the change in thickness, the unipolar potential of the anode and the cathode were measured. The measurement result of the unipolar potential of is described.

The anode and cathode were prepared by the procedure described below.

Anode: Fannes Black catalyst powder (3 with wet reduction of platinum and ruthenium in an atomic ratio of 1: 1)
0% by weight Pt supported) and Polyflon Dispersion D-
1 (manufactured by Daikin Industries, Ltd.) was added, and the amount of polytetrafluoroethylene (hereinafter abbreviated as PTFE) was 30% by weight.
The resulting kneaded product is applied to a carbon paper base material (4 mg PTFE / cm ² ) which has been previously treated with PTFE,
It was calcined in air at 300 ° C. for 30 minutes.

Carsword: A catalyst powder (30% by weight Pt supported) obtained by wet reduction of platinum on a furnace black and a kneaded product in which PTFE is 30% by weight are added to a carbon paper base material (8 mgPTFE / cm ² ) which has been previously treated with PTFE. It was applied and baked in air at 300 ° C. for 30 minutes.

Rolling was performed using the above electrode so that the initial thickness of the electrode was about 70%. In the electrode before rolling (conventional type), when the bending angle is 60 ° or more, the electrode is broken into two pieces. However, after rolling, even if a cylinder having a diameter of about 3 cm is formed, the electrode will not be damaged if electrodes having the same size are used.

With respect to the conventional electrode and the electrode of the present invention, the shapes of the carbon fibers on the surface on which the catalyst layer was not formed were taken by scanning electron microscope photographs. FIG. 3 shows a conventional electrode, and FIG. 4 shows an embodiment of the present invention. The magnification is 190 times.

In the electrode according to the present invention, the carbon battlefield is finely cut. The number of cut portions is overwhelmingly larger than that of the conventional example shown in FIG. A considerable part of the cut part of carbon fiber About 1
Polytetrafluoroethylene enters above / 3,
It acts as a binder that joins the cut carbon fibers together. The number of gaps at the interface between the carbon fiber and polytetrafluoroethylene is greater in the present invention than in the conventional example.

Scanning electron micrographs showing the shape of carbon fibers in the cross section of the electrode are shown in FIGS. 5 and 6. FIG. 5 shows a conventional electrode, and FIG. 6 shows an electrode according to the present invention. Magnification is 2
30 times.

In the conventional electrode, the catalyst layer has a thickness of about 120 μm and the substrate has a thickness of 350 μm, whereas in the electrode of the present invention, the boundary between the catalyst layer and the substrate is not clear, but the thickness of the catalyst layer is about 52 μm.
The base material thickness is about 300 μm, which is about 75% of the initial electrode thickness after rolling. Looking at this division, the change in the thickness of the catalyst layer was reduced by 43% and the change in the base material was reduced by 86%, and the thickness of the catalyst layer was significantly changed by rolling.

Next, the measurement result of the electric resistance is shown in FIG. By connexion resistance in the electrode with the pressing pressure of conventional electrodes and the invention as seen in figures differ, 3.5 Kg / cm ² at 0.1 [Omega · cm ²
Below, the value of the electrode of the present invention was slightly lower.
The measurement was based on 4-terminal measurement.

FIG. 8 shows the width of the ratio of the thicknesses measured at 10 places for the conventional electrode before rolling and the electrode after rolling. A variation of ± 10% is observed in the electrode before rolling, but the electrode thickness accuracy is significantly improved to ± 1.5% after rolling.

FIG. 9 shows the measurement results of the current density-potential characteristics of the conventional electrode before rolling and the anode according to the present invention.
The performance of the methanol electrode is better as the potential is lower. As can be seen in the figure, the electrode according to the invention is 60 mA.
It showed a good result of about 25 mV at a current density of / cm ² . Also, the difference is large on the constant current density side. As shown below, the reaction at the methanol electrode is a reaction that generates carbon dioxide CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻ . Although there are many side reactions and the reaction mechanism has not been clarified, it is considered that the change in the electrode structure according to the present invention contributes in some way and exhibits a peculiar behavior on the constant current density side.

Next, the measurement result of the cathode is shown in FIG.

As can be seen in the figure, the electrode of the present invention has a lower electric resistance than the electrode before rolling, but the performance is remarkably deteriorated on the high current density side. This is because rolling reduces the pore volume of the catalyst layer, and if a certain amount of electrolyte penetrates into the pores, the gas field forming a gas-liquid-solid three-phase interface, that is, gas diffusion is hindered. Therefore, it is considered that the performance deteriorates.

Example 3 In Example 2, it was considered that the anode and the cathode had an optimum range for consolidation of the catalyst layer by rolling. Therefore, the relationship between the change law from the electrode initial thickness and the performance was measured. The result is shown in FIG. The potential in the figure is the current density 60.
It is a value when it is mA / cm ² . Regarding the anode, it shows a substantially constant potential at 80% to 60% of the initial electrode thickness, which is improved by about 25 mV as compared with the conventional electrode. On the other hand, with respect to the cathode, there is little change up to about 80%, but if it exceeds this value, the performance will drop significantly. From the above results, 60 to 80% of the initial thickness of the electrode in the anode,
It was found that the cathode had a limit of 80%.

FIG. 12 shows the measurement results of the current density-potential characteristics of the air electrode having a thickness of 80% after rolling. The same characteristics as the conventional electrode before rolling shown in FIG. 10 were obtained.

Example 4 In this example, the current density-voltage characteristics of a single cell were measured using the anode according to the present invention obtained in FIG. 9 and the cathode obtained in FIG. The result is shown in FIG. The figure also shows the unit cell characteristics of the electrodes that have been used conventionally. The effective electrode area of the battery used in this example is 25 cm.
² and the anolyte used as fuel is 1.0mo
l / CH is _{3 OH-1.5mol / H 2 SO} 4, measurement temperature was 60 ° C..

The characteristics of the cathode according to the present invention are almost the same as those of the conventional electrode, and only the anode is improved by about 25 mV at a current density of 60 mA / cm ² . However, when used as a battery, it showed a voltage 15 mV higher than the single electrode potential difference, that is, 40 mV (60 mA / cm ² ) higher than the conventional battery. It is considered that this is because the electrode was made compact to exhibit flexibility, and the electrode thickness was kept constant, so that the adhesion between the electrode, the ion exchange membrane, and the current collector plate was increased.

Example 5 This example relates to a life test of the unit cell obtained in Example 1. The operation is a measurement of the voltage change at a constant current density discharge of 60 mA / cm ² . The temperature is 60 ° C, and anolyte is 1.0 mol / CH ₃ OH-1.5.
mol / H ₂ SO ₄ . The battery according to the present invention showed a voltage about 40 mV higher than that of the conventional electrode battery, and both showed a voltage drop of about 10 mV after 500 hours from the initial voltage, but almost stable results were obtained.

〔The invention's effect〕

According to the method of the present invention, since sufficient flexibility can be imparted to the electrodes, the adhesion around the electrodes can be improved and the battery performance can be improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the structure of a methanol fuel cell according to an embodiment of the present invention, FIG. 2 is a characteristic view showing the relationship between electric resistance and pressing pressure for various carbon substrates, and FIG.
FIG. 4 is a scanning electron microscope photograph showing the carbon fiber shape of the carbon substrate in the conventional electrode, FIG. 4 is a scanning electron microscope photograph showing the carbon fiber shape of the electrode according to the present invention, and FIG. 5 is a cross section of the conventional electrode. A scanning electron micrograph showing the carbon fiber shape, FIG. 6 is a scanning electron micrograph showing the carbon fiber shape of the cross section of the electrode of the present invention, FIG. 7 is an electric resistance characteristic diagram of the electrode, and FIG. FIG. 9 is a characteristic diagram showing the relationship between the measurement points and the widths of the measurement points regarding the electrode thickness, FIG. 9 is a characteristic diagram of the current density-potential of the anode, and FIG. 10 is a characteristic diagram of the current density-potential of the cathode.
The figure is a characteristic diagram showing the relationship between the consolidation ratio of the anode and the cathode and the potential, FIG. 12 is the characteristic diagram of the current density-potential of the cathode, and FIG. 13 is the characteristic diagram of the current density-voltage of the unit cell. FIG. 14 is a characteristic diagram showing the relationship between the battery voltage and the operating time. DESCRIPTION OF SYMBOLS 1 ... Fuel separation plate, 2 ... Fuel chamber, 3 ... Anode, 4 ... Conductive porous substrate, 5 ... Catalyst carrying conductive porous particle layer, 6 ...
Gas separation plate, 7 ... Oxidant chamber, 8 ... Cathode, 9 ... Conductive porous substrate, 10 ... Catalyst-supporting conductive porous particle layer, 11
… Ion exchange membrane.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Iwamoto 3-1-1, Saiwaicho, Hitachi, Ibaraki Hitachi Research Laboratory, Hitachi Ltd. (72) Inventor Tatsuo Horiba 3-chome, Hitachi-shi, Ibaraki No. 1 in Hitachi Research Laboratory, Hitachi, Ltd. (72) Teruo Kumagai, 3-1-1, Saiwaicho, Hitachi City, Ibaraki Prefecture In Hitachi Research Laboratory, Hitachi, Ltd. (72) Hiroki Tamura, Hitachi City, Ibaraki Prefecture 3-1-1, Machi, Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor, Noriko Kitami, 3-1-1, Saiwaicho, Hitachi City, Ibaraki Hitachi Research Institute, Hitachi Ltd.

Claims (24)

[Claims] 1. A carbon paper comprising carbon fibers and an organic binder, and a water repellent fired substrate comprising polytetrafluoroethylene impregnated in the voids of the carbon paper, wherein the carbon fibers have a plurality of cut portions. A water-repellent fired carbon substrate having flexibility, wherein at least one of the cut portions is impregnated with the polytetrafluoroethylene. 2. A flexible water-repellent fired carbon substrate according to claim 1, which has 20 or more cut portions of the carbon fiber per 1 mm ² . 3. A flexible water-repellent fired carbon substrate according to claim 1, which has 300 or less cut portions of the carbon fiber per 1 mm ² . 4. The flexible water-repellent firing according to claim 1, wherein the polytetrafluoroethylene is impregnated in 1/3 or more of the number of cut portions of the carbon fiber. Carbon substrate. 5. The flexible water repellent carbon substrate according to claim 1, wherein substantially all of the cut portions of the carbon fiber are impregnated with the polytetrafluoroethylene. . 6. A water-repellent fired carbon substrate having flexibility according to claim 1, wherein the substrate has a thickness of 0.1 to 1 mm. 7. The flexible structure according to claim 1, wherein a gap is provided in a part of an interface between the polytetrafluoroethylene impregnated in the void of the carbon paper and the carbon fiber. Water repellent fired carbon substrate. 8. A step of impregnating carbon paper comprising carbon fibers and an organic binder with polytetrafluoroethylene suspension, followed by firing and rolling or pressing to cut said carbon fibers and said polytetrafluoroethylene. A method for manufacturing a flexible water-repellent fired carbon substrate, which comprises a step of impregnating a part of fluoroethylene into the cut portion. 9. A method for manufacturing a water-repellent fired carbon substrate having flexibility according to claim 8, wherein the rolling or pressing is performed after the firing step is completed. 10. The flexible water-repellent firing according to claim 8, wherein the heating temperature in the firing step is in the range of the melting temperature of polytetrafluoroethylene or higher and the decomposition temperature or lower. Carbon substrate manufacturing method. 11. The method for manufacturing a water-repellent fired carbon substrate having flexibility according to claim 8, wherein the heating temperature in the firing step is in the range of 330 to 400 ° C. 12. The water-repellent fired carbon having flexibility according to claim 8, which is reduced to 60 to 80% of the plate thickness before processing by the rolling or pressing. Substrate manufacturing method. 13. A catalytically active component-supporting conductive particle and a binder are coated on a water-repellent fired substrate made of polytetrafluoroethylene impregnated in the voids of carbon paper and harmful carbon paper, which are made of carbon fiber and an organic binder. In the electrode for a fuel cell having the following catalyst layer, the carbon fiber of the fired substrate has 20 or more cut portions per mm ² .
A fuel cell electrode, wherein at least one of the cut portions is impregnated with the polytetrafluoroethylene and has flexibility. 14. The fuel cell electrode according to claim 13, wherein the fired substrate has 300 or less carbon fiber cut portions per 1 mm ² . 15. The fuel cell electrode according to claim 13, wherein the polytetrafluoroethylene is impregnated into 1/3 or more of the number of cut portions of the carbon fiber. 16. The fuel cell electrode according to claim 13, wherein the thickness of the fired substrate is 0.1 to 1 mm. 17. The fuel cell electrode according to claim 13, wherein the catalyst layer has a thickness of 0.05 to 0.5 mm. 18. The fuel cell electrode according to claim 13, wherein the catalyst layer is composed of a noble metal-supporting carbon particle selected from Group VIII of the Periodic Table of Elements and a binder. 19. A pair of electrodes facing each other, an electrolyte located between the pair of electrodes, a fuel chamber adjacent to an anode of the pair of electrodes, and an oxidant chamber adjacent to a cathode of the pair of electrodes, A pair of electrodes is composed of carbon paper consisting of carbon fibers and a binder, a water repellent fired substrate consisting of polytetrafluoroethylene impregnated in the voids of the carbon paper, and a catalyst layer formed at least on the electrolyte side of the substrate. In the fuel cell in which the catalyst layer is composed of conductive particles carrying a catalytically active component and a binder, at least one carbon fiber of the calcined substrate has 20 or more cut portions per 1 mm ² , and At least one of the fuel cells is impregnated with the polytetrafluoroethylene. 20. The methanol fuel cell according to claim 19, wherein anolyte containing methanol is supplied to the fuel chamber. 21. The methanol fuel cell according to claim 20, wherein the catalyst layer of the cathode has a larger pore diameter and / or pore volume than the catalyst layer of the anode. 22. The methanol fuel cell according to claim 20, further comprising an ion exchange membrane containing an electrolyte between the pair of electrodes. 23. The fuel cell according to claim 19, wherein the carbon fiber has not more than 300 cut portions per 1 mm ² . 24. The fuel cell according to claim 19, comprising a cell having a laminated structure in which a plurality of unit cells each having the pair of electrodes, the fuel chamber and the oxidant are laminated.