JPH06223835A - Gas diffusion electrode - Google Patents

Abstract

(57) [Summary] [Purpose] The gas diffusion electrode has a large thickness in order to secure a passage for the gas to enter, and since it contains a large amount of an insulating binder, it is electrically conductive. Was inferior. Therefore, a gas diffusion electrode having improved conductivity is provided. [Structure] A gas diffusion electrode is composed of the gas supply layer 4, the catalyst layer 3, and the current collector plate 5. The catalyst layer 3 is the gas supply layer 4
The current collector plate 5 is joined to one side of the gas supply layer 4, and the current collector plate 5 is joined to the other side of the gas supply layer 4. The gas supply layer 4 contains fine powder of metal or metal oxide having good conductivity and corrosion resistance. This gas diffusion electrode has a low specific resistance when collecting current.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas diffusion electrode applicable to a fuel cell, a secondary battery, an electrochemical reactor and an electrode for electrolysis, which has a reduced current collecting resistance.

[0002]

2. Description of the Related Art A general structure of a gas diffusion electrode used in a fuel cell or the like is shown in FIG. In FIG. 1, 11 is a gas supply layer, 12 is a catalyst layer, and 13 is a current collector plate.
1, the catalyst layer 12 is bonded to one side of the gas supply layer 11
The current collector plate 13 is joined to the other side of the. Water repellent carbon and an insulating binder are used as constituent materials of the gas supply layer 11, and hydrophilic carbon to which a catalyst is adhered and an insulating binder are used as constituent materials of the catalyst layer 12. Is used. Such a gas diffusion electrode is
For example, JP-A-63-245863 and JP-A-62.
-29069, JP-A-62-154571 and the like.

[0003]

In order to efficiently collect the electricity generated at the joint portion between the catalyst layer and the gas supply layer by the collector plate joined to the gas supply layer, the gas supply layer has a low resistance. Must. However, the gas supply layer is configured to have a large thickness in order to secure a passage for gas to enter, and since the gas supply layer contains a large amount of an insulating binder, the gas diffusion layer has a conductive property. There was a problem that was inferior.

Therefore, the present invention aims to provide a gas diffusion electrode having improved conductivity.

[0005]

In order to solve the above-mentioned problems, the present invention comprises a gas supply layer, a catalyst layer, and a current collector plate, and the catalyst layer is provided on one side of the gas supply layer. In a gas diffusion electrode for a fuel cell having a structure in which the current collector plate is bonded to the other side of the gas supply layer, a metal or metal oxide having good electrical conductivity and corrosion resistance in the gas supply layer. The gas diffusion electrode is characterized in that the current collecting resistance is reduced by containing the fine powder of.

[0006]

With carbon powder (graphite) and RuO ₂ , the specific resistance of carbon is about 30 times higher, so fine powder of metal or metal oxide having good electrical conductivity and corrosion resistance should be used in the gas supply layer. By including it, the current collecting resistance of the gas diffusion electrode can be reduced.

[0007]

Example 1 As the metal or metal oxide used in the present invention, those having good electrical conductivity and corrosion resistance are suitable, for example, their names and their general resistance values (specific resistance). For example, RuO ₂ (3-5 × 10 ⁻⁵ Ω
.Cm), IrO ₂ (3-6 × 10 ⁻⁵ Ω · cm), Os
O ₂ (6 × 10 ⁻⁵ Ω · cm), Ru (7 × 10 ⁻⁶ Ω · c)
m), Ta (12.5 × 10 ⁻⁶ Ω · cm), Mo (5.
2 × 10 ⁻⁶ Ω · cm) and the like.

The significance of adding a metal or a metal oxide is that their resistance values are much smaller than that of carbon powder as an electrode material. For example, in RuO ₂ , the specific resistance is higher than that of carbon powder (in the case of graphite). Is about 1/30, the specific resistance is small, the specific gravity is smaller than that of carbon powder (in the case of graphite), and the thickness of the manufactured electrode can be reduced.

Next, the present invention will be described in more detail with reference to the drawings. FIG. 2 shows an example of a methanol fuel cell using the gas diffusion electrode of the present invention. In FIG. 2, 6 is a methanol electrode composed of a gas diffusion electrode, and 7 is an air electrode facing it. An electrolyte chamber 8 is formed between the methanol electrode 6 and the air electrode 7, and a fuel chamber 9 is formed on the other side of the methanol electrode 6.
However, an air chamber 10 is formed on the other side of the air electrode 7.

FIG. 3 shows an enlargement of a portion A in FIG.
As shown in FIG. 3, the methanol electrode 6 serving as a gas diffusion electrode includes a catalyst layer 3 (left half), a gas supply layer 4 (right half), and a current collector plate 5. The catalyst layer 3 is a semi-water repellent porous body or fine powder catalyst layer 3 obtained by dispersing and mixing an insulating water-repellent resin in a conductive porous body or fine powder carrying the catalyst 2 and binding them. can get. The catalyst layer 3 is composed of a hydrophilic portion that can be impregnated with an electrolytic solution and a water repellent portion that serves as a gas passage.

For the gas supply layer 4, a water-repellent resin is dispersed and mixed in a conductive porous body or fine powder which does not carry the catalyst 2, and the mixture is made of a metal or a metal having good electrical conductivity and corrosion resistance. Obtained by adding a fine powder of oxide. The gas diffusion electrode of the present invention is formed by first joining the catalyst layer 3, the gas supply layer 4 and the SUS current collector plate 5 by cold pressing, and then joining them by hot pressing. To be done.

Polytetrafluoroethylene (abbreviated as PTFE) or the like is used as the water-repellent resin, and carbon black or the like is used as the conductive fine powder. Further, a fine powder of metal or metal oxide (Ru) having good electrical conductivity and corrosion resistance is added to a mixture of PTFE and carbon black.
O ₂ , IrO ₂ , OsO ₂ , Ru, Ta, Mo, etc.) are added.

When the amount of the fine powder of metal or metal oxide having good electrical conductivity and corrosion resistance is about 10% by weight with respect to the mixture of PTFE and carbon black, the current collecting resistance is the lowest. Very optimal. (1) Method for preparing RuO ₂ fine powder-added gas supply layer A water-repellent carbon black fine powder and a PTFE fine powder having a weight ratio of 3.5: 6.5 are previously dispersed in water, and ultrasonically dispersed using water as a solvent. A raw material dispersion liquid was obtained.

Next, the raw material dispersion liquid was filtered and dried to prepare a cake. The RuO ₂ fine powder having an average particle diameter of 1 to 3 μm was added to the dry cake so that the addition amounts thereof were 0, 5, 10, 15, and 20% by weight, respectively. Prepare each kind,
After kneading, it was rolled to form a sheet and dried.

(2) Preparation method of raw material for catalyst layer Pt-supported hydrophilic carbon black fine powder and P
The water-repellent carbon black fine powder carrying TFE was mixed in a mixer at a weight ratio of 6: 4. (3) Electrode assembly method After cold pressing the sheet of the gas supply layer prepared in the above (1) and the SUS current collector at 400 kg / cm ² , the gas supply layer was prepared in the above (2). The catalyst layers (powder mixture) prepared above are stacked and cold pressed again at 100 kg / cm ² .

Japanese Patent Application No. 4-22 is used as the SUS current collector plate.
No. 3737 current collector plate, that is, a current collector plate having a plurality of conductive mesh openings and conductive plate-shaped portions, the plate-shaped portions forming the periphery of the openings. To use.
Next, for the purpose of melting the binder contained in each layer, that is, PTFE, and fixing the whole electrode, the whole electrode is 345
Hot press at 5 ° C. and 5 kg / cm ² .

(4) Comparative data of resistance value As described above, the RuO ₂ fine powder was added to the gas supply layer in an amount of 5, 10, 1 with respect to the total weight of the dried cake.
The resistance value of the electrode as a whole made of an electrode made of an additive amount of 5,20% by weight and an electrode made of an additive-free material of RuO ₂ fine powder is 2MH ₂ SO ₄
The specific resistance value shown in the following Table 1 was obtained by the current interruption method. In addition, the measured value in this case does not consider the thickness of the electrode, and the area resistance value (unit: Ω · c
m ² ) was obtained. The experimental results in Table 1 are shown as a graph in FIG.

[0018]

[Table 1]

According to Table 1, the specific resistance value decreased as the amount of the RuO ₂ fine powder added to the total weight of the dry cake gradually increased, and the minimum specific resistance value was obtained at 10% by weight. When the amount of RuO ₂ fine powder added exceeds 10% by weight, the specific resistance value gradually increases.
It is understood that when the content exceeds 5% by weight, the resistance value becomes higher than that in the case where it is not added, so that there is no effect of addition.

[0020]

EFFECTS OF THE INVENTION It is possible to provide a gas diffusion electrode for a fuel cell which is not affected by an electrolytic solution and has a lower specific resistance when collecting current.

[Brief description of drawings]

FIG. 1 shows a general structure of a gas diffusion electrode used in a fuel cell or the like.

FIG. 2 shows an example of a methanol fuel cell using the gas diffusion electrode of the present invention.

FIG. 3 shows a gas diffusion electrode of the present invention.

FIG. 4 is a graph showing the effect of addition of the RuO ₂ fine powder on the specific resistance.

[Explanation of symbols]

1 CO ₂ 2 catalyst 3 catalyst layer 4 gas supply layer 5 current collector plate 6 methanol electrode 7 air electrode 8 electrolyte chamber 9 fuel chamber 10 air chamber

Claims (1)

[Claims] 1. A gas supply layer, a catalyst layer, and a current collector plate, wherein the catalyst layer is joined to one side of the gas supply layer, and the current collector plate is attached to the other side of the gas supply layer. In a gas diffusion electrode for a fuel cell having a joined structure, it is possible to reduce the current collecting resistance by including fine powder of metal or metal oxide having good electrical conductivity and corrosion resistance in the gas supply layer. Characteristic gas diffusion electrode.