JPH08117598A - Catalyst for high-molecular solid electrolytic type fuel cell - Google Patents

Abstract

PURPOSE: To provide an electrode catalyst for polymer solid electrolytic type fuel cell achieving high activation by properly selecting a physical property of a carrier in stead of selecting expensive catalyst metal to improve activation although an influence of solid property of the carrier to the activation has not always been considered with respect to a conventional electrode catalyst for polymer solid electrolytic type fuel cell. CONSTITUTION: An electrode catalyst for polymer solid electrolytic type fuel cell uses a hard graphic carbon black having a relative surface area of 250-350 m<2> /g, a particle size of 150-350 Å, a catalyst carrier amount of 20-55 wt.% based on the carrier, or an easy graphic carbon black having a relative surface area of 900-1,500 m<2> /g, a particle size of 200-400 Å, of a catalyst carrier amount of 20-55 wt.% based on the carrier. By using the black carbon having physical properties in this range, a higher activation electrode catalyst for polymer solid electric type fuel cell than by using the conventional carbon black is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell catalyst in which platinum or a platinum alloy is supported on a non-graphitizable or graphitizable carbon black carrier used as an electrode of a polymer electrolyte fuel cell.

[0002]

2. Description of the Related Art Electrochemical cells, such as polymer electrolyte fuel cells, are attracting attention as a power source for electric vehicles and spacecraft because they are more compact and have higher current densities than phosphoric acid fuel cells. . Also, in the development of this field, various electrode structures, catalyst production methods, system configurations, etc. have been proposed. The electrode structure of the conventional solid polymer electrolyte fuel cell is, for example, a collector for cathode / cathode / solid polymer electrolyte (ion exchange membrane)
/ Anode / Anode current collector has a five-layer sandwich structure.

In producing the electrodes for the fuel cell, that is, the anode and the cathode, particular attention should be paid to the prevention of poisoning of the electrodes by carbon monoxide contained in the supplied fuel and the activity per unit amount of catalytic metal. It is to raise. Conventionally, in order to avoid the poisoning and increase the activation, it has been earnestly attempted to select a supported catalyst metal and support it as a plain or alloy, and a high-performance fuel cell catalyst and electrode have been put into practical use.

On the other hand, the carbon carrier, which is another component of the fuel cell catalyst, is considered to have little or no contribution to the activity, and the fact is that little consideration is given to the improvement of the carbon carrier. In view of such circumstances, the applicant of the present invention examined various physical properties of the carbon support and found that a certain range of apparent density had a good effect on the activity (JP-A-6-103984). Regarding the specific surface area, which is the main physical property of the carrier, it was recognized that the larger the specific surface area, the smaller the particle size of the catalyst particles obtained, but no further consideration has been made.

[0005]

SUMMARY OF THE INVENTION The present inventors have completed the present invention by discovering that among the physical properties of carbon carriers, there are physical properties other than the above-mentioned apparent specific gravity that can enhance the activity. Another object of the present invention is to provide a catalyst for a polymer solid oxide fuel cell having a higher activity by using a carbon black carrier having physical properties different from those of conventional carbon black carriers.

[0006]

The polymer solid oxide fuel cell catalyst according to the present invention has a specific surface area of 250 when the carrier is a non-graphitizable carbon black.
˜350 m ² / g, particle size 150˜350 Å, catalyst loading on the carrier is 20˜55% by weight, and the specific surface area is 90 when the carrier is graphitizable carbon black.
The catalyst has a particle size of 0 to 1500 m ² / g, a particle size of 200 to 400 Å, and a catalyst loading amount of 20 to 55% by weight relative to the carrier.

The details of the present invention will be described below. There are several types of carbon black, among which there are non-graphitizable carbon black and easily graphitizable carbon black. The former carbon black is an acetylene type and has a property that it is not easily graphitized when burned, and the latter carbon black is a furnace type and has a property that it is graphitized relatively easily by burning. Conventionally, these carbon blacks have been used as a carrier for an electrode catalyst for a fuel cell, but the contribution of the physical properties of the carbon black to the catalytic activity was hardly considered.

The present inventor has made various studies on carbon black having physical properties which have not been conventionally used as a carrier for an electrode catalyst for a polymer electrolyte fuel cell. As a result, carbon black having a certain range of physical properties was used as a carrier. It has been found that the performance as a polymer electrolyte fuel cell is remarkably improved by using it as. That is, in the case of non-graphitizable carbon black, the specific surface area of the carbon black carrier (specific surface area measured by the BET method) is
250 to 350 m ² / g, particle size of 150 to 350 Å, platinum or platinum alloy loading amount in the range of 20 to 55% by weight with respect to the carrier, and in the case of graphitizing property, specific surface area of carbon black carrier Is 900-1500 m ² / g, particle size is 150-350 Å
High activity can be obtained when the amount of platinum or platinum alloy supported is within the range of 20 to 55% by weight based on the carrier. In the case of using a platinum alloy, the alloy forming metal is selected from noble metals such as palladium and rhodium and base metals such as tin in consideration of improvement of activity and prevention of carbon monoxide poisoning.

The specific surface area of the carbon black carrier and the particle size thereof have a certain degree of correlation, and when one increases, the other tends to decrease, but both carbon blacks have the specific surface area and particle size within the above range. When the platinum or platinum alloy is loaded, the catalyst particles having the optimal particle size are loaded on the carrier having the optimal particle size, and the best activity is obtained. The optimal, in other words, the particle size of the catalyst particles with the highest activity is about 20 to 37 Å. If it is less than this range, the activity tends to decrease, and if it exceeds this range, the specific surface area of the entire catalyst particles decreases greatly Leads to a decline.

When the particle size of the carbon black carrier becomes large, the specific surface area becomes small, the number of catalyst particles supported on the carrier becomes small, and the particle size of the catalyst particles becomes large, so that it is difficult to enter the above range. Activity tends to decrease.
Conversely, when the particle size of the carrier becomes smaller, the specific surface area becomes larger,
The number of catalyst particles supported on the carrier increases, the particle size of the catalyst particles decreases, and the activity increases. The catalyst loading amount of platinum or platinum alloy per unit carrier amount is 20 to 55%, and if it exceeds this value, the particle size becomes large and non-uniform, while if it is less than this value, the particle size becomes small and the activity becomes low. It does not fall within the particle size range of the catalyst particles.

Other physical properties that affect the catalytic activity include interlayer distance (Co / 2), DBP oil absorption and heat treatment temperature. The interlayer distance is the distance between the adjacent lattice layers composed of carbon atoms. If this distance is too small, the corrosion resistance of carbon black is lost and the particle size of the catalyst particles increases, so it is desirable to maintain at least 3.4. Also DBP
The oil absorption amount is the amount of oil that the carbon black carrier absorbs when it is impregnated with the carrier, and the larger this value is, the larger the space in the carbon black is. Gas permeability is poor, and if this value is too large, a large amount of electrolyte is required. Therefore, the DBP oil absorption is preferably 200 to 650 ml / 100 g-carbon black.

Further, the heat treatment temperature influences the degree of agglomeration of the resulting catalyst particles. If the temperature is high, the agglomeration proceeds and the particle size becomes too large, and if it is too low, the particle size becomes excessively small. It is desirable to set the temperature to ~ 750 ° C. In this way, the catalyst for polymer solid oxide fuel cells produced by supporting the catalyst particles such as platinum on the carbon black carrier is usually 30 to 60% by weight, preferably 45 to 55% by weight with respect to the catalyst. % Nafion (manufactured by DuPont) and other ion-exchange resins are supported on a porous current collector such as carbon paper to form a solid polymer electrolyte fuel cell electrode with the highest gas permeability and high activity. can do.

[0013]

EXAMPLES Examples of the fuel cell catalyst according to the present invention will be described below, but the present examples are not intended to limit the present invention.

[Example 1] Specific surface area of carbon black carrier is 1475 m
² / g, carbon black particle size 150Å, interlayer distance (C
o / 2) is 3.56Å and DBP oil absorption is 330 ml /
100 g of Cabot Corporation's easily graphitizable carbon black BP-2000 was suspended in a chloroplatinic acid aqueous solution (platinum concentration: 7 g / liter) and heated at 85 to 90 ° C.
After stirring for 30 minutes, it was cooled to room temperature.

Reducing agent sodium thiosulfate (Na ₂ S ₂ O
₃ ) 10 ml was added at once, and after 5 minutes, 65 ml was added, and the mixture was vigorously stirred for 10 minutes with a homogenizer, filtered and dried. Then, heat treatment was performed at 450 ° C. in a nitrogen atmosphere containing 50% by weight of hydrogen (platinum loading: 40% by weight). Further, it was dipped in a commercially available ion exchange resin dispersion (Nafion solution) and dispersed using an ultrasonic homogenizer to produce a paste (amount of Nafion: 50% by weight based on the carbon black carrier). This paste was spread on a carbon paper which was treated to be water repellent with polytetrafluoroethylene (PTFE), and used as a cathode for a fuel cell. The platinum particle size of this cathode was measured and found to be 26
Was Å.

Instead of the above-mentioned BP-2000, the carbon black carrier has a specific surface area of 300 m ² / g, a carbon black particle size of 300 Å and an interlayer distance (Co / 2) of 3.59 Å.
Non-graphitizable carbon black AB- manufactured by Denki Kagaku Kogyo Co., Ltd., which has a P oil absorption of 390 ml / 100 g
An electrode was prepared in the same manner using 12, and the cathode and the anode were integrated with a Nafion membrane, which is an ion exchange membrane manufactured by DuPont, sandwiched therebetween to form a fuel cell. This fuel cell was operated at 60 ° C and the current densities at 0.9 V and 0.7 V were measured.
It was 95 mA / cm ² and 910 mA / cm ² .

[0016]

[Example 2] As a cathode carrier, the carbon black carrier has a specific surface area of 1310 m ² / g, a carbon black particle size of 300 Å, an interlayer distance (Co / 2) of 3.60 Å, and a DBP oil absorption of 500 ml / 100 g. Graphite carbon black Ketjenblack EC600 JD manufactured by Mitsubishi Petrochemical Co., Ltd. was used and the heat treatment temperature was 700 ° C.
A cathode and an anode were prepared and a fuel cell was constructed in the same manner as in Example 1 except that the above was adopted (amount of platinum carried: 40% by weight). The platinum particle size of this cathode was measured and found to be 21Å. Operate this fuel cell at 60 ℃,
When the current density at 0.9 V and 0.7 V was measured,
^They were 102 mA / cm ² and 970 mA / cm ² , respectively.

[0017]

Example 3 A cathode and an anode were prepared and a fuel cell was constructed in the same manner as in Example 1 except that the above-mentioned non-graphitizable carbon black AB-12 was used as a cathode carrier. Amount: 30% by weight). The platinum particle size of this cathode was measured and found to be 35Å
Met. This fuel cell is operated at 60 ° C, 0.9 V and
When the current density at 0.7 V was measured, it was 90
mA / cm ² and 860 mA / cm ² .

[0018]

[Comparative Example 1] As a cathode carrier, a carbon black carrier has a specific surface area of 1500 m ² / g, a carbon black particle size of 150 Å, an interlayer distance (Co / 2) of 3.84 Å and a DBP oil absorption of 360 ml / 100 g. A cathode and an anode were prepared and a fuel cell was constructed in the same manner as in Example 1 except that the easily graphitizable carbon black M-3950 manufactured by Mitsubishi Kasei Co., Ltd. was used and the heat treatment temperature was 480 ° C. (Platinum loading: 20% by weight). The platinum particle size of this cathode was measured and found to be 15Å. When this fuel cell was operated at 60 ° C. and the current densities at 0.9 V and 0.7 V were measured, they were 48 mA / cm ² respectively.
And 350 mA / cm ² .

[0019]

[Comparative Example 2] As a cathode carrier, the carbon black carrier has a specific surface area of 800 m ² / g, a carbon black particle size of 300 Å, an interlayer distance (Co / 2) of 3.59 Å and a DBP oil absorption of 365 ml / 100. A cathode and an anode were prepared in the same manner as in Example 1 except that the graphitizable carbon black Ketjen Black EC manufactured by Mitsubishi Petrochemical Co., Ltd. (g) was used and the heat treatment temperature was 450 ° C. A battery was constructed (platinum loading: 20% by weight). The platinum particle size of this cathode was measured and found to be 18
Was Å. This fuel cell was operated at 60 ° C and the current densities at 0.9 V and 0.7 V were measured.
It was 68 mA / cm ² and 500 mA / cm ² .

[0020]

[Comparative Example 3] As a cathode carrier, the carbon black carrier has a specific surface area of 1120 m ² / g, a carbon black particle size of 220 Å, an interlayer distance (Co / 2) of 3.66 Å and a DBP oil absorption of 420 ml / 100 g. A cathode and an anode were prepared in the same manner as in Example 1 except that the non-graphitizable carbon black AB-7 manufactured by Denki Kagaku Kogyo Co., Ltd. was used and the heat treatment temperature was 450 ° C.
In addition, a fuel cell was constructed (platinum loading: 40% by weight). The platinum particle size of this cathode was measured and found to be 50Å. This fuel cell is operated at 60 ℃, 0.9 V and 0.7 V
The current density was measured to be 46 mA /
cm ² and 500 mA / cm ² .

The physical properties and the like of the carbon blacks used in Examples 1 to 3 and Comparative Examples 1 to 3 are summarized in Table 1 (the graphitizable carbon black is referred to as CB, and the graphitizable carbon black is referred to as CB. Omitted).

[0022]

[Table 1]

As can be seen by comparing Examples 1 to 3 and Comparative Examples 1 to 3, even if the same kind of non-graphitizable or graphitizable carbon black is used as a carrier,
If the physical properties, especially the specific surface area and the particle size are different, a large difference occurs in the obtained current density. For example, when using easily graphitizable carbon black as a carrier, when the carrier specific surface area is 900 to 1500 m ² / g and the carrier particle size is 200 to 400 Å (Examples 1 and 2), the current density is 0.9 V and 95 ~ 102 m
A / cm ² is high, but the upper limit of specific surface area is 1500
When it reaches m ² / g (Comparative Example 1), the current density that can be taken out is greatly reduced. Similarly, when using non-graphitizable carbon black as a carrier, the carrier specific surface area is 250
When maintained in the range of ~ 350 m ² / g (Example 3), a high current density can be obtained, whereas when the specific surface area is exceeded (Comparative Examples 2 and 3), the current density that can be taken out is greatly reduced. To do.

[0024]

Industrial Applicability The present invention provides a catalyst for polymer solid oxide fuel cells, which comprises platinum or platinum alloy catalyst particles supported on a non-graphitizable carbon black carrier, and the non-graphitizable carbon black carrier has a specific surface area of 250. ~
A catalyst for a fuel cell, which is characterized by having 350 m ² / g, a particle size of 150 to 350 Å, and an amount of supported catalyst of 20 to 55% by weight with respect to the carrier. a specific surface area of 900 ~1500m ² / g, particle size 200-400
Å The amount of catalyst supported on the carrier is 20 to 55% by weight (claim 2).

[0025] In the conventional non-graphitizable carbon black and the graphitizable carbon black carrier, the influence of the physical properties of carbon black on the activity etc. has hardly been studied. The present inventor examined the physical properties of each carbon black, particularly the specific surface area, particle size and amount of catalyst supported on the carbon black, and found that the catalyst for polymer solid oxide fuel cells produced by the physical properties of the carbon black used. It has been found that the activity as an electrode when the electrode is formed by using is greatly changed. Therefore, according to the present invention, by the simple method of selecting the physical properties of the carrier,
Since the activity of the electrode catalyst can be improved, an economically highly active fuel cell can be provided.

In addition to the specific surface area and the like, the interlayer distance of carbon black and the DBP oil absorption amount also affect the activity of the fuel cell electrode catalyst, the former interlayer distance is 3.4 or more (claim 3), and the latter DBP oil absorption amount. When it is 200 to 650 ml, even higher activity can be obtained.

 ─────────────────────────────────────────────────── ─── Continued Front Page (71) Applicant 391016716 STONHART Associates Incorporated STONEHART ASSOCIATES INCORPORATED USA 06443 Connecticut, Madison, Cottage Road 17, P-O Box 1220 (72) Inventor Yumi Yamamoto 2-7 Shinmachi, Hiratsuka-shi, Japan Tanaka Kikinzoku Kogyo Co., Ltd. Technology Development Center

Claims (4)

[Claims] 1. A fuel cell catalyst comprising a non-graphitizable carbon black carrier carrying platinum or platinum alloy catalyst particles, wherein the non-graphitizable carbon black carrier has a specific surface area of 250 to 350 m ² / g and a particle size. Is 150-35
A catalyst for a polymer electrolyte fuel cell, wherein the amount of supported catalyst is 20 to 55% by weight based on the carrier. 2. A fuel cell catalyst comprising a graphitizable carbon black carrier carrying platinum or platinum alloy catalyst particles, wherein the graphitizable carbon black carrier has a specific surface area of 900 to 1500 m ² / g and a particle size of 200-40
A catalyst for a polymer electrolyte fuel cell, wherein the amount of supported catalyst is 20 to 55% by weight based on the carrier. 3. The catalyst for polymer electrolyte fuel cell according to claim 2, wherein the interlayer distance of carbon black is 3.4 or more. 4. The DBP oil absorption of carbon black is 200.
The catalyst for polymer solid oxide fuel cells according to claim 2 or 3, wherein the catalyst is about 650 ml.