JP2003089968A - Carbon fiber cloth, gas diffusion material, membrane- electrode junction, and fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon fiber cloth 2 having excellent water-controlling characteristics without being deteriorated in electrical conductivity, to provide a gas diffusion material 1, to provide a membrane-electrode junction 4 given by using the same, and to provide a fuel cell. SOLUTION: This carbon fiber cloth 2 is formed by gathering two or more fiber elements of the carbon fiber, wherein oxygen atoms exist on the surface of the carbon fiber in a ratio of not less that 0.06 but less than 0.17 in number based on carbon atoms. The carbon fiber cloth 2 is given by a production method which includes at least a process for subjecting the carbon fiber cloth formed by gathering two or more fiber elements of the carbon fiber to electrolytic treatment.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a carbon fiber cloth, a gas diffuser, which is particularly preferably used as a material for an electrode in a polymer electrolyte fuel cell, a membrane-electrode assembly using the same, and a fuel cell. It is a thing.

[0002]

2. Description of the Related Art A polymer electrolyte fuel cell is a stack of a plurality of membrane-electrode assemblies (MEA) sandwiched by separators on both sides with a gasket interposed therebetween. MEA
Is composed of an anode electrode and a cathode electrode in which a reaction responsible for power generation takes place, and a solid polymer electrolyte membrane sandwiched between both electrodes. The electrode comprises a catalyst layer and a gas diffuser.

In general, a gas containing hydrogen and oxygen is supplied to the anode and cathode electrodes to carry out the following reaction.

Anode reaction: H ₂ → 2H ⁺ + 2e ⁻ (1) Cathode reaction: 2H ⁺ + 2e ⁻ + (1/2) O ₂ → H ₂ O (2) Equation (1) is the reaction at the anode electrode, Equation (2) represents the reaction at the cathode electrode. Since water is generated at the cathode by the reaction, unless the generated water is efficiently discharged out of the system, water is clogged at the cathode electrode, gas diffusivity is lowered, and oxygen necessary for the reaction cannot be sufficiently supplied.

Further, the proton conductivity of the solid polymer electrolyte membrane that transfers protons from the anode side to the cathode side decreases unless it is in a wet state. In order to maintain the proton conductivity of the solid polymer electrolyte membrane, a method of humidifying the gas supplied to the anode and the cathode is generally adopted.

As described above, in order to efficiently discharge the water generated at the cathode and to keep the solid polymer electrolyte membrane in a wet state, it is very important to manage water in the system in the polymer electrolyte fuel cell. .

As a material for an electrode of a polymer electrolyte fuel cell, a base material such as carbon paper or carbon fiber woven fabric is often used. BACKGROUND ART Heretofore, in a polymer electrolyte fuel cell, hydrophilic treatment of a base material has been performed for the purpose of appropriate water management (Japanese Patent Laid-Open No. 9-245800, US Pat. No. 5,292,600, etc.). For example, Japanese Patent Laid-Open No. 9-245
In Japanese Patent Publication No. 800, by using a carbon fiber woven fabric that has been subjected to hydrophilic treatment with SiO ₂ , the discharge property of the generated water in the cathode electrode of the fuel cell and the water supply property to the electrolyte layer are improved, and the gas permeability of the electrode is secured. is doing.

[0008]

However, since the carbon fiber woven fabric is subjected to hydrophilic treatment, Si having a very low conductivity is used.
When O ₂ is used, the conductivity of the base material is reduced, which causes a problem that the performance of the fuel cell is reduced.

The present invention overcomes the drawbacks of the prior art, does not impair the conductivity, and has excellent water management characteristics, a carbon fiber cloth, a gas diffuser, and a high-performance membrane-electrode assembly using the same. The purpose is to provide a fuel cell.

[0010]

In the present invention, the above object is a cloth composed of a plurality of carbon fibers aggregated, and the ratio of the number of oxygen atoms to the number of carbon atoms on the surface of the carbon fibers is 0.06. It is achieved by the carbon fiber cloth which is not less than 0.17.

When the above carbon fiber cloth is used as a gas diffuser, it is preferable to have a carbon layer containing carbon black and a fluororesin on at least one surface of the carbon fiber cloth.

The weight ratio of the fluororesin contained in the carbon layer to the carbon black is 0.01 or more and 0.70.
The following is preferable.

Using the above gas diffuser, a membrane-electrode assembly having a catalyst layer containing catalyst-supporting carbon on both surfaces of a solid polymer electrolyte membrane and further having a gas diffuser in contact with both catalyst layers is provided. Can be created. The membrane-electrode assembly can be used in a fuel cell.

The carbon fiber cloth can be obtained by a manufacturing method characterized in that it has at least a step of electrolytically treating a carbon fiber cloth formed by assembling a plurality of carbon fibers.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing an example of a gas diffuser proposed in the present invention. A gas diffuser 1 according to the present invention has a carbon fiber cloth 2 formed by assembling a plurality of carbon fibers as a base material in FIG. 1, and has a carbon layer 3 containing carbon black and a fluororesin on at least one surface thereof. .

The carbon fiber cloth 2 refers to a woven fabric or a non-woven fabric formed by assembling a plurality of carbon fibers. The carbon fiber fabric may be spun yarn fabric or filament fabric. The carbon fiber non-woven fabric preferably retains its shape by the entanglement of fibers, and is preferably of a type that does not use adhesive fibers or adhesives.

The carbon fiber cloth 2 has a basis weight of 50 to 2
00 g / m ² , a thickness of 150 to 400 μm, and a woven fabric of yarn having a weaving density of 10 to 30 yarns / cm in both the longitudinal direction and the transverse direction are more preferable, and a basis weight is 80 to 150 g /
More preferred is a spun yarn woven fabric having m ² , a thickness of 200 to 300 μm, and a yarn weaving density in the range of 15 to 25 yarns / cm in both the longitudinal direction and the transverse direction. The thickness of the carbon fiber cloth is the thickness when the surface pressure is 0.15 MPa.

On the surface of the fibers constituting the carbon fiber cloth 2,
The ratio of the number of oxygen atoms to the number of carbon atoms is 0.06 or more.
It is preferably less than 17, and 0.10 or more and 0.16
The following is more preferable, and 0.11 or more and 0.15 or less is further preferable.

The ratio (O / C) of the number of oxygen atoms to the number of carbon atoms on the carbon fiber surface of the carbon fiber cloth is defined by the following equation.

O / C = (ratio of oxygen atoms on the fiber surface)
/ (Ratio of carbon atoms on the fiber surface) When the O / C of the carbon fiber surface is less than 0.06, the hydrophilicity of the fiber surface becomes poor, and the mobility of water in the yarn by the capillary formed by multiple carbon fibers. Tends to decrease. Therefore, excess water in the system cannot be efficiently discharged, water produced by the power generation reaction accumulates, and there is a tendency that the gas diffusivity decreases due to water clogging of the cathode electrode. O of carbon fiber surface
When C is 0.17 or more, the hydrophilicity of the fiber surface is too high, so that the gas diffusion tends to be deteriorated due to the clogging of the cathode electrode even when the amount of produced water is small. In the carbon fiber cloth 2 according to the present invention, since the fiber surface has an appropriate hydrophilicity, the mobility of water in the cloth by the capillaries formed by a plurality of carbon fibers is high, which causes water clogging of the cathode electrode. It has the characteristic of being difficult. for that reason,
Excessive water in the system can be discharged efficiently, and it has excellent water management characteristics.

The ratio of carbon atoms and oxygen atoms on the carbon fiber surface can be measured by X-ray photoelectron spectroscopy.

In the carbon fiber cloth 2 according to the present invention, carbon atoms on the fiber surface and atoms for improving hydrophilicity are bonded by a chemical bond, so that compared with the case where a hydrophilic agent such as SiO ₂ is attached. It is characterized by high chemical stability. Therefore, when the fuel cell is operated for a long period of time, the effect that the hydrophilicity of the carbon fiber surface is unlikely to decrease with time can be expected.

Further, in the case of the present invention in which atoms such as oxygen are introduced onto the fiber surface in order to improve the hydrophilicity on the surface of the carbon fiber, a hydrophilic agent such as SiO _{2 having} very low conductivity is conventionally attached. Compared with the technique, it has an effect that the conductivity of the carbon fiber cloth having hydrophilicity on the surface of the fiber is less deteriorated.

The gas diffuser 1 according to the present invention preferably has a carbon layer 3 containing a fluororesin and carbon black on at least one surface of the carbon fiber cloth 2.
The weight ratio of the fluororesin contained in the carbon layer 3 to carbon black is preferably 0.01 or more and 0.70 or less, more preferably 0.05 or more and 0.60 or less, and 0.1
It is more preferably 0 or more and 0.40 or less. When the weight ratio of the fluororesin contained in the carbon layer to the carbon black is smaller than 0.01, there is a problem that the binder effect of the fluororesin connecting the carbon blacks becomes small and the carbon layer becomes brittle. Then, there is a problem that the ratio of the fluororesin having a very low conductivity increases, and the conductivity of the gas diffuser is greatly reduced.

Here, the fluororesin means tetrafluoroethylene resin (PTFE), perfluoroalkoxy resin (PFA), fluorinated ethylene propylene resin (FE).
P), fluorinated ethylene tetrafluoroethylene resin (E
It refers to a water-repellent resin containing a fluororesin in its structure, such as TFE).

Since the gas diffuser 1 according to the present invention uses the above carbon fiber cloth 2, it has excellent water management characteristics.

By providing the carbon layer 3 on at least one side of the carbon fiber cloth 2, the surface of the gas diffuser 1 becomes smooth and it is easy to secure electrical contact. It also has the effect of preventing the gas diffuser from sticking into the solid polymer electrolyte membrane and causing a short circuit when the membrane-electrode assembly (MEA) is produced.

Next, the membrane-electrode assembly (MEA) 4 proposed by the present invention will be described with reference to FIG.
In FIG. 2, the MEA 4 has a catalyst layer 6 on both surfaces of the solid polymer electrolyte membrane 5, and further has a gas diffuser 1 in contact with both the catalyst layers 6 and 6. MEA according to the present invention
4 uses the gas diffuser 1 on at least one side of both gas diffusers 6, 6. Further, it is preferable that the side on which the gas diffuser 1 is used is the cathode side. The catalyst layer 6 is
It is composed of a layer containing a solid polymer electrolyte and catalyst supporting carbon. It is desirable to use platinum as the catalyst. When the reformed gas containing carbon monoxide is supplied to the anode side, it is desirable to use platinum and ruthenium as the catalyst on the anode side. The solid polymer electrolyte 5 is preferably made of a perfluorosulfonic acid-based polymer having high ion permeability, oxidation resistance, and heat resistance.

Membrane-electrode assembly (MEA) 4 according to the present invention
Since the above gas diffuser 1 having excellent water management characteristics is used at least on the cathode side, it is unlikely to be clogged with water generated by the power generation reaction, and exhibits extremely high battery characteristics.

The polymer electrolyte fuel cell according to the present invention is a stack of a plurality of membrane-electrode assemblies (MEA) 4 shown in FIG. is there. Since the above-mentioned membrane MEA4 that exhibits extremely high cell characteristics is used, the fuel cell proposed by the present invention exhibits extremely high performance.

Next, a method of manufacturing the carbon fiber cloth 2 proposed in the present invention will be described with reference to FIG. Figure 3
[Fig. 3] is a process drawing schematically showing a method for manufacturing the carbon fiber cloth 2 proposed in the present invention.

In FIG. 3, first, in the preparation step (A), a cloth (a carbon fiber cloth 7 before electrolytic treatment) such as a woven fabric or a non-woven fabric formed by collecting a plurality of carbon fibers is manufactured. In the preparation step (A), the carbon fibers may be woven or non-woven into a cloth shape, or the carbonizable precursor fibers may be woven or non-woven into a cloth shape and then carbonized.

For example, in the case of producing a carbon fiber spun yarn woven fabric, the carbonizable precursor fibers are thinly aligned in a certain direction and arranged, and twisted to obtain spinning. The spun yarn woven fabric obtained by weaving the obtained spun yarn is carbonized at 1000 to 3000 ° C. under an inert atmosphere such as nitrogen to obtain a carbon fiber spun yarn woven fabric.

When producing a carbon fiber woven nonwoven fabric, a web of carbonizable fibers is randomly and uniformly placed on a net, and the fibers are entangled to obtain a nonwoven fabric. The obtained non-woven fabric is 1000 to 300 under an inert atmosphere such as nitrogen.
A carbon fiber non-woven fabric is obtained by carbonizing at 0 ° C. As a method for making carbon fibers into a non-woven fabric, spun lace in which the fibers are entangled with a high-pressure water stream, needle punching in which the web is entangled by needling the web, and the like are preferable.

In the electrolytic treatment step (B), the carbon fiber cloth 7 before electrolytic treatment obtained in the step (A) is electrolytically treated in the electrolytic bath 8 to introduce oxygen atoms into the carbon fiber surface. The electrolytic solution 9 used for the electrolytic treatment is sulfuric acid, nitric acid, hydrochloric acid,
An aqueous solution containing an electrolyte containing no metal cation such as ammonia or ammonium chloride as a solute is preferable. The metal cation causes a decrease in proton conductivity of the solid polymer electrolyte membrane 5 and the solid polymer electrolyte contained in the catalyst layer 6. The electrolytic solution 9 is more preferably an aqueous solution containing, as a solute, an electrolyte such as sulfuric acid, nitric acid, or hydrochloric acid whose cation when ionized is a proton. Even if protons remain in the obtained carbon fiber cloth 2, the proton conductivity of the solid polymer electrolyte membrane 5 and the solid polymer electrolyte contained in the catalyst layer 6 does not decrease.

Since the purpose of the step (B) is to introduce oxygen atoms into the carbon fiber surface, it is preferable to dispose the carbon fiber cloth 7 on the side of the anode 11 where the oxygen atoms are reduced.

The current density during the electrolytic treatment is 0.01 to
1.00 A / g-carbon fiber cloth is preferable, and 0.02-
0.50 A / g-carbon fiber cloth is more preferable, and 0.0
5 to 0.30 A / g-carbon fiber cloth is more preferable.
When the current density is smaller than 0.01 A / g-carbon fiber cloth, the time required to perform the necessary oxidation treatment becomes long, and when the current density is larger than 1.00 A / g-carbon fiber cloth, oxygen introduced to the carbon fiber surface. There is a problem in that the density of atoms is uneven.

In the post-treatment step (C), the carbon fiber cloth electrolytically treated in the step (B) is washed with purified water or the like. After washing, the cloth is dried to obtain the carbon fiber cloth 2 proposed in the present invention.

In the method for producing the carbon fiber cloth 2 according to the present invention, since the electrolytic treatment is carried out in order to introduce oxygen atoms into the carbon fiber surface, the carbon fiber cloth is oxidized by oxygen in the air or steam. It can be processed at a lower temperature than the method. The method of oxidizing a carbon fiber cloth with oxygen in the air or water vapor has a problem that the temperature required for the reaction is high, the progress of the oxidation reaction is rapid, and control is difficult. According to the present invention, the amount of oxygen atoms introduced onto the carbon fiber surface can be easily controlled by the current density and the treatment time during treatment.

[0040]

Example 1 Example 1 500 ml of 0.1N sulfuric acid was placed in a beaker, a carbon plate was used for the cathode 12 and 8 cm × 8 for the anode 11.
Carbon fiber woven fabric Avcarb 107
1HCB Fabric (TEXTRON System
Electrolysis treatment was performed using ms Corporation). The electrolytic treatment was carried out at a current of 56.3 mA (current density of 0.
08 A / g-carbon fiber cloth) for 63 seconds. After washing the carbon fiber woven fabric after electrolytic treatment with purified water,
The hydrophilically treated carbon fiber woven fabric 2 was obtained by drying in an oven at 100 ° C. for 10 minutes.

The carbon fiber woven fabric 2 obtained above was applied with a thickness of 20.
The carbon coating liquid was applied using a spacer made using a 0 μm polyester film and a stainless steel plate having a thickness of 1 mm. The applied carbon coating liquid is
Solid content is acetylene black (Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd.), PTFE (using Polyflon PTFE Dispersion D-1 manufactured by Daikin Industries, Ltd.), surfactant (TRITON X-114 manufactured by Nacalai Tesque, Inc.)
Was added, and the ratio was adjusted to 4: 1: 8. Purified water was further added to adjust the solid content to 20.0 wt% of the whole. Carbon fiber woven fabric provided with carbon layer 3,
After a desurfactant treatment in an oven at 380 ° C. for 30 minutes, hot pressing was performed for 5 minutes by a batch press at a temperature of 200 ° C. and a surface pressure of 3 MPa, to obtain a gas diffuser 1.

Platinum-supporting carbon (Tanaka Kikinzoku Co., Ltd., platinum content 50% by weight) 1.00 g, purified water 1.00 g, Nafi
on solution (Nafion 5.0 manufactured by Aldrich)
(Wt%) 8.00 g and isopropyl alcohol (manufactured by Nacalai Tesque, Inc.) 18.00 g were sequentially added and sufficiently stirred with a homogenizer to prepare a catalyst coating liquid.

On a PTFE sheet (Naflon tape TOMBO9001 manufactured by Nichias), the above catalyst coating solution was applied in an amount of 5
P ² with a catalyst layer having a platinum amount of 0.5 mg / cm ² was obtained by spraying on a square of cm ² and drying.
A TFE sheet was obtained. Solid polymer electrolyte membrane 5 (Nafion 1 manufactured by DuPont) cut into 5 cm × 5 cm
12) is sandwiched between the above PTFE sheets with catalyst layers, and 13
The catalyst layer 6 was transferred to the solid polymer electrolyte membrane 5 by batch pressing at 0 ° C. and 5 MPa for 5 minutes. After pressing
The PTFE sheet was peeled off to obtain a solid polymer electrolyte membrane with a catalyst layer.

Two pieces each having a square size of 5 cm ² were cut out from the gas diffuser 1. The above-mentioned solid polymer electrolyte membrane with a catalyst layer was sandwiched between the cut gas diffusers 1 and batch-pressed at 130 ° C. and 2 MPa for 5 minutes to obtain membrane-electrode assemblies (MEA) 4. The gas diffuser 1 was arranged so that the surface having the carbon layer 3 was in contact with the catalyst layer 6 side.

The obtained MEA 4 was incorporated in a fuel cell evaluation unit cell, hydrogen and air were supplied under normal pressure, and the current-voltage (IV) characteristic was measured under the condition of an operating temperature of 70 ° C. Hydrogen and air were humidified by a humidification pot set at 80 ° C and 60 ° C, respectively. The utilization rates of hydrogen and air were 70% and 40%, respectively. The voltage value at 1 A / cm ² of the fuel cell using the MEA was 0.474V.

Hydrophilically treated carbon fiber fabric 2 to 2.0c
A sample of m × 2.5 cm was sampled and sandwiched between ^two carbon plates, and a voltage V (V) between them was measured under a pressure of 98 N / cm ² with a current of 1 A applied between the carbon plates. . The electrical resistance R (mΩ · cm ² ) in the thickness direction of the hydrophilically treated carbon fiber woven fabric 2 at that time was calculated by the following formula.

R = V × 2.0 × 2.5 × 1000 The calculated electric resistance was 11 mΩ · cm ² .

The fiber surface composition of the hydrophilically treated carbon fiber woven fabric 2 was measured by X-ray spectroscopy, and the ratio (O / C) of the number of oxygen atoms to the number of carbon atoms on the fiber surface was calculated to be 0.09. Met.

Example 2 A hydrophilically treated carbon fiber woven fabric 2 was obtained in the same manner as in Example 1. However, in the electrolytic treatment, only the time of passing the current was changed from 63 seconds to 125 seconds,
All other conditions were the same.

Using the obtained hydrophilically treated carbon fiber woven fabric 2, a gas diffuser 1 and a membrane-electrode assembly (MEA) 4 were prepared in the same manner as in Example 1.

The voltage value at 1 A / cm ² of the fuel cell using the MEA 4 was measured by the same method as in Example 1 and found to be 0.522V.

When the electric resistance in the thickness direction of the hydrophilically treated carbon fiber woven fabric 2 was measured by the same method as in Example 1, it was 11 mΩ · cm ² .

The fiber surface composition of the hydrophilically treated carbon fiber woven fabric 2 was measured by X-ray spectroscopy and the ratio of the number of oxygen atoms to the number of carbon atoms (O / C) on the fiber surface was calculated to be 0. It was 12.

Example 3 A hydrophilically treated carbon fiber woven fabric 2 was obtained in the same manner as in Example 1. However, in the electrolytic treatment, only the time of passing the current is changed from 63 seconds to 250 seconds,
All other conditions were the same.

Using the obtained hydrophilically treated carbon fiber woven fabric 2, a gas diffuser 1 and a membrane-electrode assembly (MEA) 4 were prepared in the same manner as in Example 1.

When the voltage value at 1 A / cm ² of the fuel cell using the MEA 4 was measured by the same method as in Example 1, it was 0.560V.

When the electric resistance in the thickness direction of the hydrophilically treated carbon fiber woven fabric 2 was measured by the same method as in Example 1, it was 11 mΩ · cm ² .

The composition of the fiber surface of the hydrophilically treated carbon fiber woven fabric 2 was measured by X-ray spectroscopy, and the ratio (O / C) of the number of oxygen atoms to the number of carbon atoms on the fiber surface was calculated. It was 14.

Example 4 A hydrophilically treated carbon fiber woven fabric 2 was obtained in the same manner as in Example 1. However, in the electrolytic treatment, only the time of passing the current is changed from 63 seconds to 375 seconds,
All other conditions were the same.

Using the obtained hydrophilically treated carbon fiber woven fabric 2, a gas diffuser 1 and a membrane-electrode assembly (MEA) 4 were prepared in the same manner as in Example 1.

When the voltage value at 1 A / cm ² of the fuel cell using the MEA 4 was measured by the same method as in Example 1, it was 0.502 V.

When the electric resistance in the thickness direction of the hydrophilically treated carbon fiber woven fabric 2 was measured by the same method as in Example 1, it was 12 mΩ · cm ² .

The fiber surface composition of the hydrophilically treated carbon fiber woven fabric 2 was measured by X-ray spectroscopy, and the ratio (O / C) of the number of oxygen atoms to the number of carbon atoms on the fiber surface was calculated. It was 16.

Comparative Example 1 Carbon fiber woven fabric Avcarb
1071HCB Fabric (TEXTRON S
8cm x 8) (made by systems Corporation)
Cut to cm.

Example 1 was carried out using the obtained carbon fiber woven fabric.
A gas diffuser and a membrane-electrode assembly (MEA) were prepared by the same method as described above.

When the voltage value at 1 A / cm ² of the fuel cell using the MEA was measured by the same method as in Example 1, it was 0.466V.

When the electric resistance in the thickness direction of the carbon fiber woven fabric was measured by the same method as in Example 1, it was 11 mΩ · cm.
^{Was 2} .

The fiber surface composition of the carbon fiber woven fabric was measured by X-ray spectroscopy, and the ratio of the number of oxygen atoms to the number of carbon atoms (O / C) on the fiber surface was calculated to be 0.0.
It was 5.

Comparative Example 2 A hydrophilically treated carbon fiber woven fabric was obtained in the same manner as in Example 1. However, only the time of passing the current in the electrolytic treatment was changed from 63 seconds to 500 seconds, and all other conditions were the same.

Using the obtained hydrophilically treated carbon fiber woven fabric, a gas diffuser and a membrane-electrode assembly (MEA) were prepared in the same manner as in Example 1.

When the voltage value at 1 A / cm ² of the fuel cell using the MEA was measured by the same method as in Example 1, it was 0.444V.

The electrical resistance in the thickness direction of the hydrophilically treated carbon fiber woven fabric was measured by the same method as in Example 1.
It was 4 mΩ · cm ² .

The fiber surface composition of the hydrophilically treated carbon fiber woven fabric was measured by X-ray spectroscopy, and the ratio (O / C) of the number of oxygen atoms to the number of carbon atoms on the fiber surface was calculated to be 0.17. Met.

The above Examples 1 to 4 and Comparative Examples 1 and 2
Of the ratio of the number of oxygen atoms to the number of carbon atoms on the carbon fiber surface (O / C), the electrical resistance in the thickness direction of the carbon fiber fabric, and the fuel cell using the membrane-electrode assembly (MEA) of 1 A / cm.
Table 1 shows a summary of the measurement results of the voltage values in ² .

[0075]

[Table 1]

As shown in Table 1, there is almost no decrease in conductivity due to the introduction of oxygen atoms on the carbon fiber surface.

Further, since the carbon fiber woven fabrics of Examples 1 to 4 and the gas diffusers using them were excellent in water management characteristics, the membrane-electrode assembly (MEA) using them was a very high battery. It shows the characteristics.

Therefore, an object of the present invention is to provide a carbon fiber cloth excellent in water management characteristics without impairing conductivity, a gas diffuser, a high-performance membrane-electrode assembly using the same, and a fuel cell. A carbon fiber cloth comprising a plurality of carbon fibers assembled together, wherein the ratio of the number of oxygen atoms to the number of carbon atoms on the surface of the carbon fibers is 0.06 or more and less than 0.17. To be achieved.

The carbon fiber cloth can be obtained by a method for producing a carbon fiber cloth, which has at least a step of electrolytically treating a carbon fiber cloth formed by assembling a plurality of carbon fibers.

[0080]

EFFECTS OF THE INVENTION The carbon fiber cloth provided by the present invention has a suitable hydrophilicity on the fiber surface, so that the mobility of water in the cloth by the capillaries formed by a plurality of carbon fibers is high and the cathode electrode It is hard to cause water clogging. for that reason,
Excessive water in the system can be discharged efficiently, and it has excellent water management characteristics.

Further, according to the present invention in which atoms such as oxygen are introduced on the surface of the carbon fiber in order to improve the hydrophilicity on the surface of the carbon fiber, the conductivity of the carbon fiber cloth to which the hydrophilic property is imparted is less likely to decrease.

Therefore, according to the present invention, it is possible to provide a carbon fiber cloth, a gas diffuser, a high-performance membrane-electrode assembly, and a fuel cell which have excellent water management characteristics without impairing conductivity. .

The carbon fiber cloth can be obtained by a method for producing a carbon fiber cloth, which has at least a step of electrolytically treating a carbon fiber cloth formed by assembling a plurality of carbon fibers.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a gas diffuser proposed by the present invention.

FIG. 2 is a cross-sectional view of a membrane-electrode assembly (MEA) proposed in the present invention.

FIG. 3 is a process diagram schematically showing a carbon fiber cloth proposed by the present invention.

[Explanation of symbols] 1: Gas diffuser 2: Carbon fiber cloth 3: Carbon layer 4: Membrane-electrode assembly (MEA) 5: Solid polymer electrolyte membrane 6: Catalyst layer 7: Carbon fiber cloth before electrolytic treatment 8: Electrolyzer 9: Electrolyte 10: Power supply 11: Anode 12: cathode

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01M 8/10 H01M 8/10 // H01M 8/04 8/04 K F term (reference) 4L031 AA27 CA02 CB10 DA00 DA08 4L048 AA05 AA52 AA53 AB01 AB07 AB12 AC13 AC14 CA05 CA06 DA24 5H018 AA06 AS02 AS03 BB01 BB03 BB06 BB08 BB13 BB17 CC06 DD06 DD08 EE03 EE05 EE08 EE17 EE17 EE17 H0526H0526H0526H0526H0526H0526A05AX 06A05 AH0626A05AH06A05

Claims (6)

[Claims] 1. A fabric formed by assembling a plurality of carbon fibers, wherein the ratio of the number of oxygen atoms to the number of carbon atoms on the surface of the carbon fibers is 0.06 or more and less than 0.17. Carbon fiber cloth. 2. A gas diffuser having a carbon layer containing carbon black and a fluororesin on at least one surface of the carbon fiber cloth according to claim 1. 3. The weight ratio of the fluororesin contained in the carbon layer to carbon black is 0.01 or more and 0.70.
The gas diffusion body according to claim 2, wherein: 4. A membrane-electrode assembly having a catalyst layer containing catalyst-carrying carbon on both surfaces of a solid polymer electrolyte membrane, and further comprising a gas diffuser in contact with both catalyst layers, wherein both the gases are provided. A membrane-electrode assembly, wherein the gas diffuser according to claim 2 or 3 is used on at least one side of the diffuser. 5. A fuel cell comprising the membrane-electrode assembly according to claim 4. 6. A method for producing a carbon fiber cloth, which comprises at least a step of electrolytically treating a carbon fiber cloth formed by assembling a plurality of carbon fibers.