JPS61147460A - Electrode substrate for fuel cell and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a substrate for a fuel cell having flexibility which has low resistance and good water repellent property by fixing and holding divided carbon fiber pieces by means of PTFE etc. CONSTITUTION:After a bonding agent such as PTFE etc. is impregnated into a carbon paper which is a conductive porous substrate for a fuel cell, this is rolled to 20-70% of the initial thickness of the substrate. Whereby, the carbon fibers are finely cut. Soft PTFE forms a continuous layer between the cut carbon fibers and is fixed. In such a manner, when the carbon fibers are finely cut, each carbon fiber piece has connecting points with adjacent other carbon fibers, and these connecting points are more than the connecting points of the carbon fibers before rolling. Accordingly, the resistance value becomes lower than that of the substrate before rolling. And hard and brittle carbon fibers are finely cut, whereby the substrate has flexibility. Further, water repellent property becomes good by using the carbon paper in an electrode substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an electrode substrate for a fuel cell and a method for manufacturing the same, and more particularly to a flexible electrode substrate for a fuel cell and a method for manufacturing the same.

[Background of the invention]

Fuel cells, which supply fuel and oxidizer and cause an electrochemical reaction to occur on electrodes to directly extract electrical energy, are attracting attention as a new type of power source that is expected to be highly efficient.

As shown in FIG. 5, this fuel cell is a unit cell consisting of an electrolysis chamber 3 (for example, an ion exchange membrane containing sulfuric acid) sandwiched between a fuel electrode 1 and an oxidizer electrode 2, and a current collector (not shown). is constructed by stacking a plurality of them with separators 4 interposed therebetween. Electrode l.

2 supports on a conductive porous substrate a catalyst layer 6 containing at least one component of Groups 1 and 2 of the periodic law, for example, a platinum metal element as a main component, or on a conductive porous carrier. The catalyst is coated on the substrate and bonded thereto. When forming a unit battery having such an electrode or stacking unit cells to form a battery, sufficient tightening is required to reduce contact resistance. Therefore, as a result of the electrode 1.2 being pressed against the separator 4, the electrode made of carbon paper, which is a hard and brittle substrate, is partially damaged, causing the catalyst to peel off, the electrolyte to leak into the oxidizing agent supply path 6, etc. There is a risk that the battery performance will deteriorate. In particular, because methanol/air acid electrolyte fuel cells, which are small portable power sources that use liquid as fuel, are used as mobile power sources, there is a need for a variety of battery shapes and for electrodes to be durable against vibrations during use. Ru. Conventionally used electrodes are made by coating catalyst particles together with a binder on carbon paper, which is a conductive porous substrate, and then firing the coating. The carbon paper, which is the substrate that makes up this electrode, is made entirely of carbonaceous material and is not attacked by electrolyte, has excellent heat resistance, and improves the mechanical strength of the substrate. In order to achieve this, PTFE was fixed to the carbon paper base material. However, it is treated at high temperature to reduce electrical resistance)1. The result is a hard and brittle material.

Therefore, it is necessary to prevent damage to the electrode, especially the substrate, and for this reason, a flexible substrate exists.

Carbon felt is one such substrate, but this carbon felt is a raw material in the first stage of manufacturing carbon paper, and because it contains many organic substances as impurities, it has an electrical resistance of 1 gcrr&! This is high (10 to 50 times that of carbon paper). Therefore, the output decreases due to IR loss only in the substrate, and it cannot be said to be a practical substrate. Further, such carbon felt has a large contact resistance when connected to an electrolyte plate or a separator.

Although carbon film also has flexibility, it has the same drawbacks as carbon felt.

Other flexible substrates for fuel cells include those disclosed in Japanese Patent Laid-Open No. 57-30270. This substrate is made of polytetrafluoroethylene (hereinafter referred to as PT).
The structure is such that conductive carbon powder (furnace black) is embedded between the porous meshes of 70 to sowt% PTFE fibers (referred to as FE). A catalyst component is supported on this substrate to form an electrode. However, in this type of board, the electrical resistance is 0.1 due to the rounding using PTFE fiber.
6g3! Furthermore, since the structure of the PTFE porous network changes due to thermal history, etc., there is a possibility that the carbon carrier in the network may peel off, resulting in a decrease in battery performance. Nine, PTF is used in fuel electrodes of fuel cells that use liquid fuel as raw material.
There is a possibility that the water repellency due to E is too strong, resulting in a decrease in the reaction area. In other words, although this type of fuel cell electrode substrate is useful in that it is flexible, it has often had the problem of not being able to exhibit sufficient cell performance.

[Purpose of the invention]

An object of the present invention is to provide a fuel cell electrode substrate that has flexibility and can exhibit high cell performance, and a method for manufacturing the same.

[Summary of the invention]

In the present invention, FTFB, which is a water-repellent binder, is fixed to carbon paper, which is a conventionally used conductive porous substrate, and when rolled, the carbon fibers of the carbon paper are divided into a plurality of short carbon fiber pieces. The present invention attempts to obtain a flexible fuel cell electrode substrate by fixing and holding these divided carbon fiber pieces with PTFE, which is a binder for the carbon fiber pieces. Specifically, the first invention of the present application has a plurality of short carbon fiber pieces, each of which is connected to another adjacent carbon fiber piece and fixed with a binder such as PTFE. The second invention of the present application is a fuel cell electrode substrate characterized in that the carbon paper substrate is immersed in a binder such as FTFB, and then the carbon paper substrate is immersed in a carbon paper substrate having an initial substrate thickness of 20%. It is characterized in that it has a plurality of short carbon fiber pieces by rolling to ~70%, and each carbon fiber is fixed with a binder in a state where it is connected to other adjacent carbon fibers. This is a method for manufacturing an electrode substrate for a fuel cell.

In the fuel cell electrode substrate according to the present invention, since the carbon fibers constituting the electrode substrate are finely fragmented,
Electrical resistance decreases because the number of contact points on each carbon fiber piece increases and the thickness of the electrode substrate is reduced by rolling. Specifically, 0.1gcW1! The following is true. Also,
Since the electrode substrate does not use PTFE fibers but is made of carbon paper as a base material, the electrode substrate has good water repellency and can therefore be used in liquid-type fuel cells. Furthermore, since the structure is not such that carbon powder is embedded in the mesh of PTFE fibers, the problem of peeling off of the conductive material due to thermal history does not occur.

Further, since the divided carbon fibers are held and fixed by the FTFB, the fuel cell electrode substrate has flexibility. Specifically, having flexibility means that the substrate can be formed into a cylindrical shape with a diameter of 1 crn to 10 cm without damage.

In manufacturing the fuel cell electrode substrate according to the present invention, it is necessary to sinter the substrate before or after rolling after fixing PTFE to the carbon paper base material.

By firing, non-conductive organic substances contained in the carbon paper base material can be removed. To fix PTFEt to the carbon paper base material, the base material is P'
This can be done by impregnating it with rFE solution and drying it.

Rolling of carbon paper is performed by passing the carbon paper between rollers whose opening is adjusted to a certain degree. This roller opening adjustment is performed at 20 to 80% of the initial substrate thickness of the carbon paper base material. In particular, the opening degree of the rollers is preferably 60 to 80% of the initial substrate thickness in order to prevent destruction of the carbon paper and to not hinder the diffusion of fuel or oxidant gas.

An electrode is constructed by coating the electrode substrate obtained according to the present invention with a catalyst layer in which platinum, ruthenium, etc. are supported on a porous carbon carrier such as 7 Arnes black or carbon black.

The supporting method may be any of the usual catalyst preparation methods such as a deposition method, an impregnation method, an intercurrent method, and a kneading method. This catalyst powder is then mixed with distilled water and a binder such as PTF.
A catalyst paste prepared by adding Et and kneading is applied onto a t-substrate and fired with carbon to form an electrode. Since the catalyst layer on the flexible substrate has flexibility due to the binding agent, it is possible to make the entire structure extremely flexible by using such a substrate. . Note that the catalyst layer may be applied either before or after rolling with a roller, but it is preferable to apply the catalyst layer before rolling to prevent peeling of the catalyst layer and achieve rounding.

[Embodiments of the invention]

Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Figure 1 shows FT without rolling the carbon paper.
It is a microscopic photograph (Figure A) showing the microscopic structure of a conventional substrate impregnated with FB and fired, and a microscopic photograph (Fig. Figure). Note that a scanning electron microscope was used as the microscope, and the images were taken at a magnification of 300 times.

According to Fig. A, the hard and brittle carbon fibers 11 have a mesh structure), and the carbon fibers 11H are long fibers. Then, P between each carbon fiber 11
TFE 12 is intertwined and fixed.

On the other hand, according to figure B, the carbon fibers are cut into short pieces, and there is a flexible PT between the cut carbon fibers 13.
FE is bonded to form a continuous layer 14. When the carbon fibers are cut into short pieces in this manner, each carbon fiber piece has connection points with other adjacent carbon fibers, and the number of connection points is greater than the connection points of the carbon fibers before rolling. Therefore, the resistance value is lower than that of the substrate before rolling. The hard and brittle carbon fibers are broken into short pieces, giving it flexibility.

Next, specific experimental examples of the present invention will be explained.

Electrode Substrate Preparation Example 1> Carbon paper, which is a conventional conductive porous substrate, was immersed in an aqueous solution of Polyflon Dispersion D-1 (manufactured by Daikin Industries), impregnated with an FTFB amount of 4 mg/cm, dried, and then fired. Bake in a furnace at 300-400C for 1 hour.

Then, this substrate was roller rolled to about 70% of the initial substrate thickness to obtain a flexible substrate A.

Preparation Example 2 of electrode substrate Preparation Example 1 except that the carbon fiber used in the above Preparation Example was impregnated with 8 mg/cm of PTFE and fixed.
A flexible substrate B was obtained by adjusting the substrate in the same manner as described above.

Comparative Example 1> 8 m of PTFEi on a conventional carbon paper substrate
The bending limit of the flexible substrate A and B was compared with that of the substrate to which the substrate was fixed.

Even if PTFB is fixed on the conventional carbon paper substrate, 6
When the bending angle was greater than 0°, it broke into two pieces.

On the other hand, with the flexible substrates A and B, it was possible to form a cylinder with a diameter of about 5 degrees even with the same dimensions as the conventional substrate, and one substrate did not cause any damage.

<Comparative Example 2> The electrical resistances of flexible substrate B, a conventional carbon paper substrate, carbon felt, and carbon film were compared with each other. Figure 2 shows the measured values of the electrical resistance of each substrate.

In the figure, 21 is a graph showing carbon felt, 22
23 is a graph showing carbon paper, and 24 is a graph showing flexible substrate. The resistance values are in the order of decreasing resistance for the flexible substrate B, followed by carbon fiber, carbon film, and carbon felt, and increasing resistance values. The reason why carbon felt and carbon film have a high resistance value is because they contain impurity organic compounds that have a high electrical resistance due to not being fired.It is possible that the flexible substrate B has a lower electrical resistance than carbon paper. Flexible substrate Bt - 64° This is due to the fact that the constituent carbon fibers are divided into end pieces, resulting in a large number of connection points.The measurement was performed using a four-terminal measurement method (100OH2).

Catalyst preparation example 1> Carbon powder (furnace black: manufactured by Cabot) 20
Add 50ml of 37% formaldehyde solution and 100ml of 50% potassium hydroxide solution to 50ml of distilled water. This was cooled to 0±.2 C without stirring, and a solution prepared by dissolving 28 g of chloroplatinic acid and 14 g of ruthenium chloride in distilled water to give a concentration of 500° was added to this solution while maintaining the temperature at θ±20. After addition, let stand to return to room temperature, then heat to 35-40C.
Stir for 2 hours at 55-60C and further stir for about 2 hours at 55-60C. After stirring, the solids are washed with distilled water to reduce the slurry's pH.
Repeat washing until H becomes 7 or less.

After cleaning, thoroughly dry in a dryer at 60C and remove the fuel electrode catalyst A.
't-got it.

Catalyst preparation example 2> Carbon powder (furnace black: manufactured by Cabot) 15
(1:1) methanol-water was added to 1 g, then 31 g of chloroplatinic acid was dissolved therein, and the mixture was heated and stirred at 70 tl' for about 5 hours. After the stirring is completed, the solid material is washed repeatedly until the pH becomes 7 or less. The washed cake was dried at 60G to obtain oxidizer electrode catalyst B.

<Electrode Preparation Example 1> Add 1.15 g of catalyst powder A and 2-distilled water, mix well, and then mix the PTFEi used in Substrate Preparation Example 1 (manufactured by Daikin: Polyflon Dice Version D 1.2.5 times diluted). )
Add 1- and mix. This paste-like catalyst was evenly applied to a flexible substrate (100 x 128 cm), and after air drying,
Bake for about 30 minutes in a nitrogen atmosphere. With this operation,
The fuel electrode was used as an electrode person.

Electrode adjustment example 2> 4mg/cm on the conventionally used carbon paper substrate
The electrode prepared by the method of Electrode Preparation Example 1 was used as fuel electrode electrode B, except that the electrode was impregnated with the PTFB liquid.

Electrode Adjustment Example 3> After adding 0.77 g of catalyst powder B and distilled water and mixing,
Add and mix polyflon dispersion Dlt-0,55+d to flexible substrate B (100x128m)
After air drying, bake in the air for about 30 minutes. This was designated as oxidizer electrode A.

<Electrode adjustment example 4> 8mg/31 on the conventionally used carbon paper substrate
Oxidizer electrode B was an electrode prepared in the same manner as in Electrode Preparation Example 3, except that the electrode was impregnated with PTFE.

Voltage Measurement Example 1> In this measurement example, a unit cell was constructed using a fuel electrode A and an oxidizer electrode A using a flexible substrate, and its current density-voltage characteristics were measured. Between the electrodes, 3 mot
Ion exchange membrane impregnated with /L of sulfuric acid (manufactured by Syo Kasei: CM
V) was interposed as an electrolyte. Anolyte (1 mot/l methanol - 1.5 mot/L sulfuric acid) was supplied as the fuel, air was supplied as the oxidizing agent, and the unit cell temperature ti
It is 60C. The results are shown in FIG. 31.

Comparative Example 3> Current density-voltage characteristics were measured in the same manner as voltage measurement 1 except that fuel electrode B and oxidant electrode Btl were used.

The results are shown in FIG. 32.

From FIG. 3, the one using the flexible substrate according to the present invention is
j) 30mV (60mA/cm
This is because the flexibility of the substrate according to the present invention increased the adhesion of the stain electrode to the ion exchange membrane and separator.

Voltage Measurement Example 2 In this example, the unit battery used in Voltage Measurement 1 was continuously operated at a current density of 60 mA/cm. The temperature was maintained at 6 (l), and the anolyte was
/, methanol-1,5 mot/l sulfuric acid.

Comparative Example 4 The results of continuous operation for 600 hours are shown in Figure 4 41. Figure 4 42 shows the results of continuous operation performed in the same manner as Voltage Measurement Example 2, except that the unit battery of Comparative Example 3 was used. .

Figure 4 shows that both batteries stabilized when the voltage decreased by about 20 mV after 600 hours from the initial voltage, and the battery of the present invention was about 30 mV higher than the battery using the conventional carbon paper substrate. voltage was obtained.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to obtain a fuel cell substrate that has low resistance, water repellency, and good flexibility. Therefore, in a fuel cell using an electrode constructed based on the fuel cell substrate according to the present invention, good cell performance can be obtained because the electrical resistance can be reduced. Since it has good water repellency, it can also be used in liquid fuel cells.

[Brief explanation of drawings]

Figure 1 is an electron microscope photograph showing the structure of the carbon fiber of the fuel cell substrate, Figure 2 is a graph showing the relationship between the electrode substrate and resistance, and Figure 3 is a graph showing the relationship between current density and cell voltage. , FIG. 4 is a graph showing the operating time and battery voltage, and FIG. 5 is a configuration diagram showing the configuration of the Rin cell of the fuel cell. DESCRIPTION OF SYMBOLS 1... Fuel electrode, 2... Oxidizer electrode, 3... Electrolyte plate, 4... Separator, 6... Catalyst layer, 7... Fuel or oxidant gas supply groove.

Claims (1)

[Claims] 1. It has a plurality of short carbon fiber pieces, and each carbon fiber piece is fixed with a binder in a state where it is connected to another adjacent carbon fiber piece. Electrode substrate for fuel cells. 2. After dipping the carbon paper base material with a binder, the carbon paper base material is rolled to 20 to 80% of the initial thickness to form a plurality of short carbon fiber pieces. 1. A method for manufacturing an electrode substrate for a fuel cell, comprising manufacturing an electrode substrate for a fuel cell in which each piece of carbon fiber is connected to another adjacent carbon fiber piece and fixed with a binder.