JPS59181463A - Gas diffusion electrode - Google Patents

Abstract

PURPOSE:To provide a gas diffusion electrode for fuel battery which assures good contactness between electrode catalyst layer and electrolyte at the time of forming battery and forms and maintain a good reactive interface between them by adding a hydrophilic carbon powder to a catalyst black mix. CONSTITUTION:As a carbon powder which supports noble metal powder such as platinum or platinum group element used as the catalyst, a hydrophilic carbon powder is used together with the graphitized carbon powder used existingly. On the occasion of manufacturing gas diffusion electrode using such carbon powder, the powder of platinum or platinum group metral of 5-15wt% is added and mixed with the graphitized carbon powder. Moreover, the hydropholic carbon powder in the amount mentioned above is added thereto. Next, adequate amount of water is also added thereto and they are mixed and stirred sufficiently so that fine inside of carbon powder is sufficiently wet. A dispersion of flurine resin used as the binding agent is added and mixed while they are stirred and thereby a catalyst black mix can be obtained. Such black mix is applied the porous substrate and is baked. Thereafter, wanted gas diffusion electrode can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a novel gas diffusion electrode, particularly a high-temperature gas diffusion electrode which maintains a good reaction interface between an electrocatalyst or its layer and an electrolyte during battery formation. The present invention relates to high performance gas diffusion electrodes for fuel cells.

(1) Li17 [
Technical background of the invention and its problems] A concentrated acid solution such as phosphoric acid or sulfuric acid that generates electricity using hydrogen, which is obtained by reforming hydrocarbons and still contains impurities such as carbon dioxide gas, as a negative electrode active material. A fuel cell using carbon as an electrolyte is generally produced by coating a porous carbon substrate with a catalyst mixture made by binding an electrode catalyst in which a precious metal catalyst is supported on carbon powder with a binder such as a fluororesin, and then firing the mixture. A unit cell is formed by forming an electrode catalyst layer on a substrate and interposing a matrix layer holding an electrolyte as described above between a pair of gas diffusion electrodes.

Conventionally, carbon powder used as a carrier for supporting catalyst powder in gas diffusion electrodes for fuel cells has been developed. Materials such as graphite powder, acetylene black or graphitized furnace black are known to be suitable.

However, these highly graphitized carbon materials have high electrical conductivity (resistance to oxidative dissolution, i.e., oxidation resistance (2)), and were expected to have high performance and long life, but they themselves lack water repellency. In addition, since it is used in combination with a fluororesin that is inherently water repellent, the electrode catalyst or electrode catalyst layer is very difficult to wet with the electrolyte during battery formation, resulting in a narrow interface that takes part in the electromotive reaction. It was difficult to produce high-performance electrodes.

[Purpose of the invention]

Thus, the present invention solves the above-mentioned difficulties and provides a high-performance fuel that maintains the wetting of the electrode catalyst or electrode catalyst layer with the electrolytic solution (and maintains the formation of a good reaction interface between them) during battery formation. The object of the present invention is to provide a gas diffusion electrode for batteries.

[Summary of the invention]

In the present invention, a catalyst mixture consisting of an electrode catalyst in which a noble metal catalyst is supported on highly graphitized carbon powder and bound with a fluororesin is coated on a porous carbon substrate, fired, and an electrode is formed on the substrate. In a gas diffusion electrode formed with a catalyst layer, hydrophilic carbon powder is further added to the catalyst mixture to improve wetting of the electrode catalyst or the electrode catalyst layer with the electrolyte during battery formation (and to improve the wetting of the electrode catalyst or the electrode catalyst layer with the electrolyte). The object of the present invention is to provide a high-performance gas diffusion electrode for a fuel cell, which is characterized in that a good reaction interface is formed and maintained between the electrodes.

[Detailed description of the invention]

To explain the present invention in detail, the gas diffusion electrode according to the present invention uses highly graphitized carbon powder that has been conventionally used as carbon powder to support noble metal powder such as platinum or platinum group elements as a catalyst. , hydrophilic carbon powder is used.

- Generally, the hydrophilicity of carbon powder is determined by various hydrophilic functional groups on the surface of carbon powder, such as hydroxyl groups, carboxyl groups,
・The number varies depending on the amount of carbon groups, lactones, quinones, etc., and the number is highest in the order of activated carbon, carbon black, and graphite. When these carbon powders are heated, these functional groups decrease and graphitization progresses, that is, the bond distance between carbon atoms becomes shorter. For this reason, water repellency gradually becomes stronger.

In the present invention, the hydrophilicity of various carbon powders is determined by dispersing the carbon powder in water and mixing it with a fluororesin dispersion (3), applying it to carbon paper, baking it, and then applying it to this paper at 0%. Judgment is made by measuring the contact angle of a droplet when 0.5 cc of 105% phosphoric acid is dropped. When the contact angle of the droplet is small and forms an acute angle, it is considered hydrophilic, and when it forms a large and obtuse angle, it is considered water repellent. Carbon powder forms an acute contact angle and is hydrophilic, while highly graphitized crystalline carbon powder such as graphite powder or graphitized carbon black forms an obtuse contact angle and is highly water repellent.

When the contact angle of a droplet was measured as described above for various types of carbon powders that are commercially available and easily available, the contact angle of activated carbon manufactured by Kanto Kagaku Co., Ltd. was 82 to 86 degrees, and the contact angle of activated carbon manufactured by Kanto Kagaku Co., Ltd. was 82 to 86 degrees, and the contact angle of activated carbon manufactured by Kanto Kagaku Co., Ltd. The carbon powder of the company's product name C3X-99 is 72 to 88
°, it is hydrophilic and therefore has good wettability.On the other hand, the contact angle of the product name Denka Black manufactured by Tokyo Denki Kagaku Kogyo Co., Ltd. is 116 to 123 °, and the contact angle of graphite powder manufactured by Nippon Graphite Co., Ltd. The name AUP is 115-133° and the USSP is 111
Contact with angles such as ~122° (4) The corners are thick (and the water repellency becomes stronger.

Water repellency is also affected by the amount of fluororesin dispersion used as a binder, and the higher the amount, the better the water repellency will be. c.ru.

The amount of hydrophilic carbon powder added to highly water-repellent highly graphitized carbon powder is preferably in the range of 10 to 70% by volume of the former. The amount of hydrophilic carbon powder added varies depending on the type of carbon powder to be combined, but if too much hydrophilic carbon powder is mixed, wettability will improve, but resistance to oxidative dissolution will be weakened, reducing catalyst function and accelerating electrode deterioration. However, it is preferable to keep it within the above-mentioned range. When combining the two carbon powders, it is preferable to select those having similar specific surface areas.

When manufacturing gas diffusion electrodes using these carbon powders, for example, platinum or platinum group metal powder is added to highly graphitized carbon powder in an amount of 5 to 15% by weight based on the carbon powder.
Then, add the hydrophilic carbon powder in the above amount, and then add appropriate water to thoroughly wet the inside of the pores of the carbon powder (stir and mix). Fluororesins such as polytetrafluoroethylene (PTFE)
, trade name Teflon) was added and kneaded with Jf stirring to obtain a catalyst mixture.

The catalyst mixture obtained in this way is applied to a porous carbon substrate and fired to form an electrode catalyst layer.This carbon substrate is made of, for example, a bulk graphite fiber made of graphitized fiber made into a thin plate using a papermaking method. 0.28(), 60 flat carbon paper, or ribbed carbon paper can be used. When applying, for example, applying vacuum suction from the back side of the substrate and spraying from the front side can achieve good application.

Then, after pressing, the material is fired in an atmosphere of an inert gas such as helium or nitrogen to obtain the desired gas diffusion electrode.

Of course, this manufacturing method is just an example, and is not limited to this.

When using the gas diffusion electrode obtained in this way, it is possible to maintain a good reaction interface between the ameliorating liquid and the electrode catalyst or the electrode catalyst layer, resulting in a high-performance and long-life fuel cell. This is made clear by the following examples.It is understood that the present invention is not limited to these examples, and includes various other modifications and applications. Should.

[Embodiments of the invention]

Example 1 Graphite powder (USSP manufactured by Nippon Graphite Co., Ltd., average particle size 1μ,
Specific surface area: 438→/9) 15% by weight of K platinum was added to make a total amount of 207%, and to this was added 5% of hydrophilic pure water with good conductivity.
After adding 00ml of carbon powder, make sure that the inside of the pores of the carbon powder is sufficiently wet (stir thoroughly with a mixer.
12 parts by weight of polytetrafluoroethylene (PTFE) dispersion were gradually added with stirring to form a catalyst mixture.

This catalyst was coated with carbon paper (E made by Kenbetsu Kagaku Kogyo Co., Ltd.).
-71.5. Porosity 77%, thickness 0.4 tone 9 area resistance 0
．． While applying vacuum suction to the back side of 4Ωm), spray uniformly with a spray gun at a nozzle pressure of 3K9/ad.

Then, the electrode was produced by pressing with a roller at 2 Kg/cni, then drying and firing in helium gas at 330° C. for 15 minutes.

Using the electrode obtained in this way, a single cell is produced,
A mixed gas of 80% hydrogen and 20% carbon dioxide, which is a simulated natural gas reforming gas, was used as the fuel, air was used as the oxidizing agent, and phosphoric acid was used as the electrolyte, and the gas flow rate was three times the theoretical amount of the maximum polarization current value. The polarization characteristics were measured at 200° C. and normal pressure.

For comparison, a single cell was prepared using a conventional electrode prepared in the same manner as in Example 1 except that no hydrophilic carbon black powder was used, and the polarization characteristics were measured in the same manner.

The results of these measurements are also shown in the graph of FIG. In this graph, curve 1 represents a battery using the electrode of the present invention, and curve 2 represents a battery using a conventional electrode. As is clear from this, when using the electrode according to the present invention, by adding and mixing hydrophilic carbon powder,
Because we were able to maintain a good reaction interface between the electrolyte and the electrode catalyst or its layer, the polarization rate was higher when polarized at a constant flow rate than with conventional electrodes that do not use hydrophilic carbon powder. I was able to show the battery voltage.

Next, use the same two cells and have a rated current of 220 mA/aA.
Figure 2 shows the results of a comparison of the changes in battery voltage over time, that is, the life characteristics when polarized. In the figure, curve 1 shows the case of the electrode of the present invention, and curve 2 shows the case of the conventional electrode, and it is clear that the case of the present invention exhibits a longer life characteristic.

Example 2 The following highly graphitized carbon powder (contact angle is approximately 100 to
The electrodes and batteries were used in the same manner as in Example 1, except that a 120° range was used, and measurements were carried out, and the results were almost the same. Nippon Graphite Co., Ltd. A, UP (
Specific surface area 150m', #), C85PC specific surface area 200m"/?), LonzaGrap, Switzerland
H8AG-13, 14, 15, 17 manufactured by Hite (specific surface area 113.120.123.205ttt'/7 in order)
), Denka Black manufactured by Tokyo Denki Kagaku Kogyo Co., Ltd. (average particle size 4.2OA).

Specific surface area 70) I/2).

Example 3 The following hydrophilic carbon powder (contact angle ranges from about 50 to 90 degrees) was used instead of the carbon black powder in Example 1.
An electrode was obtained in the same manner as in Example 1, except that a battery was used, and measurements were performed in the same manner as in Example 1. The results were almost the same as in Example 1.

Vulcan XC-72, Vulcan XC-72
R, (specific surface performance 254 tr?/?, average particle size 30m
μ), Regal 6601 ((specific surface area 112?
? II, Q, average particle size '24 mμ), Monarcbl
loo (specific surface area 240y&/7. average particle size 1.4mμ
), Monarch 1300 (specific surface area 560 m'
/l, average particle size 13 mμ).

Example 4 In place of the carbon paper in Example 11C, carbon paper with lip (density 0.45) manufactured by Nippon Carbon Co., Ltd. was used.
f/cJ, thickness 2 holes, porosity 75-80%), electrodes and batteries were made in the same manner using the catalyst mixtures of Examples 1 to 3 and measured in the same manner. Almost similar results were obtained.

[Brief explanation of the drawing]

Figure 1 is a graph comparing the polarization characteristics of a cell using the electrode of the present invention and a cell using a conventional electrode.
The figure is a graph showing a comparison of the life characteristics of Mehaya'Kameike.

Claims (1)

[Claims] A catalyst mixture consisting of an electrode catalyst in which a precious metal catalyst is supported on highly graphitized carbon powder and bound with a fluororesin is applied to a porous carbon substrate and fired to form an electrode catalyst layer on the substrate. In the gas diffusion electrode, hydrophilic carbon powder is added to the catalyst mixture to maintain a good reaction interface between the electrode catalyst or the electrode catalyst layer and the electrolyte during battery formation. A gas diffusion electrode for fuel cells characterized by the following.