JPH05283082A - Gas diffused electrode and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide the gas diffusion electrode having the excellent gas diffus ing performance to be used for solid polyelectrolyte fuel cell. CONSTITUTION:A sheet-like reaction layer made of hydrophilic carbon black and polytetrafluoroethylene is pressed on a gas diffused layer made of porous carbon base material having water repellency by hot-pressing, or the gas diffused layer is coated with the slurry made of hydrophilic carbon black and polytetrafluoroethylene, and after the carrying, the slurry coated gas diffused layer is dried and burned to obtain a gas diffusion electrode for solid polyelectrolyte fuel cell.

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 used in a solid polymer electrolyte fuel cell and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, as a gas diffusion electrode for a fuel cell, a hydrophilic sheet made of hydrophilic carbon black and polytetrafluoroethylene and a water repellent sheet made of water repellent carbon black and polytetrafluoroethylene are used. It is formed by repeating pressure bonding and rolling a plurality of times. That is, in the conventional gas diffusion electrode, hydrophilic carbon black / polytetrafluoroethylene (weight ratio 80/20 to 50/50, preferably 70/30 to 60/40) is stirred in a solvent together with a surfactant, A hydrophilic sheet (0.2 to 0.4 mm thick) that becomes a reaction layer obtained by mixing and slurrying, filtering, drying, and pulverizing, adding a solvent again and kneading and rolling with a roll machine.
And water-repellent carbon black / polytetrafluoroethylene (weight ratio 80/20 to 50/50, preferably 75/25
-60 to 40) is stirred and mixed with a solvent together with a surface active agent to form a slurry, which is agglomerated, filtered, made into starch, added again with a solvent, kneaded, and rolled into a gas diffusion layer obtained by rolling with a roll machine. The sheet (0.5 to 2 mm thick) was overlaid and rolled by a rolling machine to a thickness of 0.5 to 0.8 mm, which was then manufactured as a drying and desurfactant.

As described above, in the conventional gas diffusion electrode for a fuel cell, the reaction layer (hydrophilic sheet) and the diffusion layer are controlled by controlling the rolling ratio before or after the hydrophilic sheet and the water-repellent sheet are superposed. The layer thickness of the (water repellent sheet) has been changed.

[0004]

The gas diffusion layer of the conventional gas diffusion electrode is formed by rolling a mixture of water-repellent carbon black and polytetrafluoroethylene by a roll method or the like into a sheet. However, the gas diffusion passage is not sufficiently secured, and since polytetrafluoroethylene is contained as a binder, there is a drawback that electrical conductivity is lowered. Also in the reaction layer, hydrophilic carbon black,
A mixture of polytetrafluoroethylene was formed into a sheet like the gas diffusion layer, and the thickness of the reaction layer due to rolling such as the roll method is limited, which greatly affects the gas diffusion of the reaction layer. It was In particular, when the above-mentioned conventional gas diffusion electrode is used as the gas diffusion electrode on the air electrode side of a solid polymer electrolyte fuel cell, there is a great effect on the gas-diffusible fuel-electric performance.

In view of the above-mentioned state of the art, the present invention solves the problems of the gas diffusion electrode used in the conventional solid polymer electrolyte fuel cell, and a gas diffusion electrode for a solid polymer electrolyte fuel cell, and a method for producing the same. Is to provide.

[0006]

The present invention provides (1) a gas diffusion layer made of a porous carbon substrate having water repellency, a hydrophilic carbon black and polytetrafluoroethylene provided on the gas diffusion layer. A gas diffusion electrode for a solid polymer electrolyte fuel cell, comprising a reaction layer comprising

(2) A sheet-like reaction layer made of hydrophilic carbon black and polytetrafluoroethylene is pressure-bonded onto the gas diffusion layer made of a porous carbon substrate having water repellency by a hot pressing method. And a method for producing a gas diffusion electrode for a solid polymer electrolyte fuel cell.

(3) A slurry-like reaction layer material composed of hydrophilic carbon black and polytetrafluoroethylene is applied on a gas diffusion layer composed of a porous carbon base material having water repellency, carried, dried and fired. A method for producing a gas diffusion electrode for a polymer electrolyte fuel cell, comprising: Is.

The water-repellent porous carbon base material which serves as the gas diffusion layer of the present invention is provided with water repellency by impregnating and supporting polytetrafluoroethylene on a porous carbon material such as carbon fiber woven fabric or carbon paper. I say what I did. As a porous carbon substrate, generally, volume resistivity: 10 ⁻³ to 10 ⁻¹ Ω−
cm, preferably 10 ⁻² to 10 ⁻³ Ω-cm, average pore diameter: 1 to 200 μm, preferably 30 to 150 μm, porosity: 20 to 80%, preferably 50 to 70%, thickness:
One having a thickness of 0.5 to 5 mm, preferably 0.7 to 2 mm is used.

The hydrophilic carbon black used as the material of the reaction layer of the present invention is a commonly used one, for example, Vulcan XC-72R (trade name: manufactured by Cabot), and the reaction layer is made of hydrophilic carbon black. A blending ratio of black / polytetrafluoroethylene (weight ratio) = 80/20 to 50/50, preferably 70/30 to 60/40 is used, and the layer thickness of the reaction layer is generally 20 to 200 μm. ,
It is preferably 40 to 100 μm.

[0011]

The gas diffusion electrode of the present invention uses a porous carbon base material as a gas diffusion layer, and therefore has a structure in which sufficient gas diffusion passages are secured, so that it is used in a solid polymer electrolyte fuel cell. In that case, the gas diffusivity is improved, and the current flowing per unit area becomes extremely large.

[0012]

【Example】

(Example 1) Average pore diameter: 40 μm, porosity: 65%,
A gas diffusion layer was obtained by subjecting a porous carbonaceous substrate having a specific resistance of 2 × 10 ^-2 Ω-cm to a moisture-proof treatment with polytetrafluoroethylene. Further, hydrophilic carbon black having an average particle diameter of 400Å and polytetrafluoroethylene having an average particle diameter of 0.3 μm are mixed in a weight ratio of 70:30, and solvent naphtha is mixed in a ratio of 1: 1.9. By mixing and rolling,
Roll forming was performed to obtain a reaction layer formed into a sheet having a thickness of 0.2 mm.

Next, the gas diffusion layer and the reaction layer are overlapped to form 3 layers.
Gas pressing electrode 1 was obtained by hot pressing at 80 ° C. and 180 kg / cm ² G.

Comparative Example 1 For comparison, average particle size: 4
20Å water repellent carbon black with an average particle size of 0.3 m
m polytetrafluoroethylene was mixed at a weight ratio of 65:35.
And mix it with solvent naphtha at a ratio of 1: 1.6.
Combined, roll-formed by roll method, thickness: 1mm sheet
A molded gas diffusion layer was obtained. Also, as in Example 1.
The reaction layer was obtained. Next, stack the gas diffusion layer and the reaction layer
Hey, 380 ℃, 180kg / cm ²Hot press with G
Then, the gas diffusion electrode 2 was obtained.

(Comparative Example 2) For further comparison, a gas diffusion layer was obtained in the same manner as in Comparative Example 1 and a reaction layer was obtained in the same manner as in Example 1. The gas diffusion layer and the reaction layer were stacked and rolled. By repeating pressure bonding and rolling by the method, a gas diffusion electrode 3 was obtained.

The gas diffusion electrodes 1, 2 and 3 thus produced
As a method for evaluating the gas diffusivity of the above, a test cell, which is schematically shown in FIG. The gas diffusivity was evaluated by measuring the analysis gas at the two outlets of the cell using a gas chromatograph to measure the diffusion into the helium flow. The results of the gas diffusivity thus obtained are shown in Table 1 as oxygen gas diffusion constants.

[0017]

[Table 1]

From the results shown in Table 1, since the gas diffusion constant corresponds to the limiting current density in the practical electrode, the gas diffusion electrode of the present invention has improved gas diffusivity, and the current flowing per unit area as the gas diffusion electrode is increased. It has a great effect.

Further, although solvent naphtha was used as the solvent in the above examples, the solvent is not limited to this, and water, ethanol, isopropyl alcohols, hydrocarbons such as n-butane may be used, and a surfactant is further added. May be.

(Example 2) Average pore diameter: 60 to 120 μm
m, porosity: 75%, specific resistance: 2 × 10 ⁻² Ω-cm, a porous carbonaceous substrate was subjected to a moisture-proof treatment with polytetrafluoroethylene to obtain a gas diffusion layer. Also, the average particle size: 4
00Å hydrophilic carbon black and average particle size: 0.3μ
Polytetrafluoroethylene of m was mixed in a weight ratio of 50:50, and water and a surfactant were added thereto to obtain a slurry.
The slurry was applied onto the gas diffusion layer by the doctor blade method, dried, and fired in a low oxygen atmosphere at 250 to 300 ° C. to obtain a gas diffusion electrode 4 having a reaction layer thickness of 20 μm.

(Example 3) In the same manner as in Example 2 above, a gas diffusion electrode 5 having a reaction layer thickness of 40 µm was obtained.

(Comparative Example 3) Water-repellent carbon black having an average particle diameter of 420Å and polytetrafluoroethylene having an average particle diameter of 0.3 mm were mixed at a weight ratio of 65:35, and solvent naphtha was mixed with 1 :. The mixture was mixed at a ratio of 1.6 and roll-molded by a roll method to obtain a gas diffusion layer molded into a sheet having a thickness of 1 mm. Further, hydrophilic carbon black having an average particle size of 400Å and polytetrafluoroethylene having an average particle size of 0.3 mm are mixed in a weight ratio of 50:50, and solvent naphtha is mixed in a ratio of 1: 1.8. The mixture was mixed and roll-formed by a roll method to obtain a reaction layer formed into a sheet having a thickness of 0.2 mm.

Next, the gas diffusion layer and the reaction layer were overlaid, and pressure bonding and rolling were repeated by a roll method to obtain a reaction layer of 150 μm.
The gas diffusion electrode 6 of was obtained.

As a method for evaluating the gas diffusivity in the gas diffusion electrodes 4, 5 and 6 produced in Examples 2 and 3 and Comparative Example 3 described above, the test cell outlined in FIG. Oxygen gas (helium gas carrier) is made to flow on one side across and the pure helium gas is made to flow on the other side, and the diffusion of oxygen gas into the pure helium flow is analyzed by gas chromatography.
The gas diffusivity was evaluated by measuring the analysis gas at two locations at the outlet of the cell. The gas diffusivity results thus obtained are shown in Table 2 as oxygen gas diffusion constants.

[0025]

[Table 2]

(Experimental Example) Platinum was suction coated on the gas diffusion electrodes 4, 5 and 6 prepared in Examples 2 and 3 and Comparative Example 3,
2 mg per apparent surface area of the electrode after oxidation and reduction treatment
Catalyst-supporting electrodes 1, 2 and 3 carrying the platinum catalyst of No. 1 were obtained. Furthermore, a solid polymer electrolyte membrane (for example, Nafio
nR117: trade name) and catalyst-supporting electrodes 1, 2 and 3 were obtained by hot pressing to obtain cells 1, 2 and 3, respectively.

Table 3 shows the results of the single cell power generation test (fuel: hydrogen, oxidizer: air) of the above cells 1, 2 and 3.

[0028]

[Table 3]

From the results shown in Table 3, it was revealed that the power generation performance of the cell using the gas diffusion electrode of the present invention was improved.

The power generation characteristics of the solid polymer electrolyte fuel cell are expressed by the following equation on the assumption that the activation overvoltage and the mass transfer overvoltage at the anode (hydrogen electrode) are ignored. E = E ₀ -blogi-iR In the above equation, E ₀ : equilibrium potential in consideration of catalytic activity,
b: Tafel coefficient, R: internal resistance {electrolyte resistance, ohmic loss current collecting resistance mass transfer (mainly reaction layer) resistance, i: current density}. The Tafel coefficient b is due to the structure factor in the reaction layer, and ideally b = 0. That is, the fact that b is small means that the gas diffusion property in the reaction layer is good.

Table 4 shows the result of analyzing the power generation test result of Table 3 by the above formula.

[0032]

[Table 4]

From the results shown in Table 4, it is clear that the present invention can reduce the thickness of the reaction layer, and thus the gas diffusivity in the reaction layer is improved.

Although water and a surfactant were used as the solvent for the slurry in Example 2 above, the present invention is not limited to this, and ethanol, isopropyl alcohol and n are used.
-Butane hydrocarbons may also be used.

[0035]

As described above in detail, according to the present invention, a gas diffusion electrode having high gas diffusivity can be provided.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of a test cell for evaluating gas diffusion of a gas diffusion electrode of the present invention.

Claims (3)

[Claims] 1. A gas diffusion layer comprising a porous carbon substrate having water repellency and a reaction layer comprising hydrophilic carbon black and polytetrafluoroethylene provided on the gas diffusion layer. A gas diffusion electrode for a solid polymer electrolyte fuel cell. 2. A sheet-like reaction layer made of hydrophilic carbon black and polytetrafluoroethylene is press-bonded onto the gas diffusion layer made of a porous carbon substrate having water repellency by a hot pressing method. Method for producing gas diffusion electrode for polymer electrolyte fuel cell. 3. A slurry-like reaction layer material composed of hydrophilic carbon black and polytetrafluoroethylene is applied and carried on a gas diffusion layer composed of a porous carbon substrate having water repellency,
A method for producing a gas diffusion electrode for a solid polymer electrolyte fuel cell, which comprises drying and firing.