JP3060683B2 - Electrode catalyst support structure, fuel cell electrode and fuel cell using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure for supporting a white metal catalyst, and more particularly to an electrode for a fuel cell using a catalyst supported by the supporting structure and a fuel cell using the electrode. .

[0002]

2. Description of the Related Art In a fuel cell in which a fuel electrode and an oxygen electrode are in contact with an electrolyte, the fuel cell depends on how efficiently the reaction at the fuel electrode and the oxygen electrode, that is, the oxidation reaction of the fuel and the ionization reaction of oxygen, are improved. Characteristics are affected. In order to increase the efficiency of these reactions, platinum, palladium,
White metal catalysts such as rhodium, ruthenium and iridium are commonly used.

As a method for supporting the platinum catalyst, A is generally used.
llen et al. (HG Petrow et al., US P. 39
92512 (1976)) or the method of Jalan et al.
Jalan et al., U.S.P. 4136059 (1979)) is used. In these methods, chloroplatinic acid is reduced with sodium hydrogen sulfite (NaHSO ₄ ) or sodium thiosulfate (Na ₂ S ₂ O ₄ ) to generate a sulfur compound of platinum in an intermediate stage, thereby suppressing grain growth of platinum. Thus, a very fine catalyst having a uniform particle size distribution can be obtained.

[0004] A method of supporting platinum on carbon will be described below as an example. First, chloroplatinic acid (H ₂ PtC
l ₆₎ was dissolved 1g of 250cc of distilled water, to which 30
After adding 10.6 cc of hydrogen peroxide of wt% while stirring, an aqueous solution of sodium thiosulfate (Na ₂ S ₂ O ₄ ) (60%) was added.
g / l) 106 cc are added with stirring to produce colloidal platinum. Using an ultrasonic stirrer, a carbon decomposition solution was prepared by sufficiently dispersing the colloidal platinum in advance so that the weight of carbon to be supported was 1 per 100 parts of distilled water, and the dispersion was heated to 60 ° C. The mixture is dropped while the platinum catalyst is supported on carbon. This platinum-carrying carbon is subjected to suction filtration and washed sufficiently with distilled water to carry the platinum on the carbon.

[0005]

SUMMARY OF THE INVENTION Such a conventional Al
The sulfur component remains in the colloidal white metal catalyst prepared by the method of Len et al. or the method of Jalan et al. When the sulfur component remains, when used as a catalyst for an electrode of a fuel cell, the electrode reaction is inhibited by sulfur, and there is a problem that the deterioration with time of the characteristics is increased. Then, a treatment for removing the residual sulfur is performed, but it is extremely difficult to completely remove the sulfur.

[0006] Further, since the colloidal platinum catalyst is simply supported by mixing with the base material, the electronic bonding between the catalyst and the base material is not sufficient, so that the resistance component in the electrode reaction increases, and at the same time the catalyst is supported. Physical peeling is likely to occur, and when a fuel cell is manufactured, there has been a number of problems that deterioration over time is greatly recognized.

It is an object of the present invention to provide an electrode catalyst supporting structure which solves the above-mentioned problems, and to provide an excellent fuel cell electrode and a fuel cell using this structure.

[0008]

According to the present invention, in order to achieve the above object, a layer mainly composed of a conductive metal oxide is formed on a conductive catalyst-supporting substrate in advance by a thermal decomposition method of an organometallic compound, This is a configuration in which the white metal catalyst is deposited on the surface of the conductive catalyst supporting base material by immersing it in a white metal chloride solution.

[0009]

According to the present invention, the white metal chloride solution improves the adhesion of the solution to these conductive substrates, and allows the catalyst to reach inside the pores existing on the surface of the conductive substrate. It becomes possible to precipitate. Moreover, since the precipitation amount of white metal is not precipitated on or formed conductive metal oxide content of the conductive base material surface, it can be white metal deposition to form a catalyst having a uniform thickness and constant Things.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram of a catalyst forming process according to an embodiment of the present invention. As shown in the figure, a metal oxide layer 2 is formed around a catalyst supporting substrate 1 and a white metal layer 3 is formed around the metal oxide layer 2.
Is carried.

FIG. 2 is a schematic diagram of an electrode configuration according to one embodiment of the present invention. As shown in the figure, the carbon electrode 4 is configured around a stainless steel mesh 5, and a lead electrode 6 is connected to the stainless steel mesh 5. A paste 7 containing carbon as a main component is formed around the carbon electrode 4, and the paste 7 is provided on both sides with an ion exchange membrane 8 interposed therebetween.

FIG. 3 is a schematic sectional view of a fuel cell according to one embodiment of the present invention. The cross section a of the polycarbonate plastic container 9 is closely adhered by bolts 10 and nuts 11. Reference numeral 12 denotes a discharge hole for water generated at the time of discharge.

(Example 1) Platinum-carbon catalyst preparation method and
And their characteristics were studied. As shown in FIG.
Specific surface area of 250 m as catalyst supporting substrate 1^Two/ G graph
Aite was used. Next, 1 mol / l of this graphite
Of zinc acetate (Zn (CH_ThreeCOO)_Two・ 2H _TwoO) Eta
After immersion in a methanol solution for 10 minutes while stirring with ultrasonic waves,
The graphite is filtered by suction and heated at 300 ° C in air.
After heat treatment, vinegar is applied to the surface as shown in FIG.
A metal oxide layer 2 mainly composed of zinc oxide is provided.
Heated in a neutral atmosphere. Then, the metal oxide layer 2
The above-mentioned graphite formed with the aqueous solution of chloroplatinic acid (3
00mg / l aqueous solution of platinum chloride adjusted to pH 5 with hydrochloric acid)
For 1 minute and deposit platinum as a white metal layer 3 on the surface
Let out.

Next, a fuel cell electrode as shown in FIG. 2 was prepared. First, carbon black having a specific surface area of 300 m ² / g was previously used as a binder and a fluororesin (trade name: Polyflon dispersion (manufactured by Daikin)) and 9: 1, 1:
After preparing two types of paste-like carbon mixed at a ratio of 1 (weight ratio), a mixture of the two types of paste-like carbon at a ratio of 1: 1 (weight ratio) is obtained as shown in FIG. The plate was press-formed into a plate shape with the stainless steel mesh 5 as the center, and the carbon electrode 4 was obtained. Around the carbon electrode 4 thus prepared, two types of paste-like graphite were prepared by previously mixing the graphite carrying platinum with the fluororesin at a ratio of 9: 1, 1: 1 (weight ratio). A mixture of these two types of pasty graphite in a ratio of 1: 1 (weight ratio) was press-formed as shown in FIG. 2 (b) to form electrodes (20 mm long, 20 mm wide, 1 mm thick).
mm).

As shown in FIG. 2 (c), the electrode thus formed was pressure-integrated using a hot press with an ion-exchange membrane (trade name: Nafion 117 (manufactured by Aldori, Inc.)) having a thickness of 130 μm. .

FIG. 3 shows the structure of a fuel cell using this integrated element. In this fuel cell, a hydrogen gas was introduced into the cathode side, and an oxygen gas was introduced into the anode side, and an operation test was performed through the external load 13. 4 and 5 show the results.

FIGS. 4A and 4B show the discharge voltage with respect to the current load. FIG. 4A shows the characteristics of the fuel cell of this embodiment, and FIG. 4B shows the characteristics of the conventional fuel cell. It is clear that the characteristics of the fuel cell of this example are excellent. This indicates that the surface area of the catalyst-carrying substrate is larger than that of the conventional one.

FIG. 5 shows the results of a continuous load test.
(A) shows the characteristics of the fuel cell of this example,
(B) shows the characteristics of the conventional fuel cell. (A)
In FIG. 3, (b) shows that the discharge voltage is temporarily lowered, while 8000 hours have passed without any trouble. This is due to the deterioration of the catalyst over time.
This example shows that the catalyst supporting structure has little deterioration over time.

Example 2 An electrode was prepared in the same manner as in Example 1 except that the supported catalyst was changed from platinum to a palladium catalyst, and a fuel cell was constructed.

The palladium catalyst is supported by a supported catalyst.
250m specific surface area^Two/ G of graphite
The graphite was treated with 1 mol / l of zinc acetate (Zn).
(CH _ThreeCOO)_Two・ 2H_TwoO) supersonic in ethanol solution
After immersing for 10 minutes while stirring with waves, absorb the graphite.
After filtration, heat treatment is performed at 300 ° C in air.
A layer mainly composed of zinc acetate on the surface of
Heated in a neutral atmosphere.

Thereafter, the carbon on which the metal oxide layer mainly composed of zinc acetate was formed was converted to a palladium chloride aqueous solution (30%).
A 0 mg / l aqueous solution of palladium chloride was adjusted to pH 5 with hydrochloric acid for 1 minute to precipitate palladium on the surface.

After the electrode was formed in the same manner as in Example 1 using the catalyst, a fuel cell was prepared and its characteristics were examined. As a result, the characteristics were exactly the same as those in Example 1.

(Example 3) An electrode was prepared in the same manner as in Example 1 except that the supported catalyst was changed from platinum to a rhodium catalyst, and a fuel cell was constructed.

For supporting the rhodium catalyst, graphite having a specific surface area of 250 m ² / g is used as the carbon to be supported, and the graphite is mixed with 1 mol / l of zinc acetate (Zn).
After immersion in an ethanol solution of (CH ₃ COO) ₂ .2H ₂ O) for 10 minutes while stirring with ultrasonic waves, the graphite was suction-filtered, and then subjected to a heat treatment at 300 ° C. in air, and zinc acetate was applied to the surface thereof. Was provided, followed by heating in a reducing atmosphere.

Thereafter, the carbon on which the metal oxide layer mainly composed of zinc acetate was formed was washed with an aqueous solution of rhodium chloride (250%).
mg / l aqueous solution of rhodium chloride adjusted to pH 5 with hydrochloric acid)
Immersion for 1 minute to deposit rhodium on the surface.

After the electrode was formed in the same manner as in Example 1 using the catalyst, a fuel cell was prepared and its characteristics were examined. As a result, the characteristics were exactly the same as those in Example 1.

Example 4 An electrode was prepared in the same manner as in Example 1 except that the supported catalyst was changed from platinum to a ruthenium catalyst, and a fuel cell was constructed.

For supporting the ruthenium catalyst, graphite having a specific surface area of 250 m ² / g was used as the carbon to be supported, and the graphite was mixed with 1 mol / l of zinc acetate (Zn).
After immersion in an ethanol solution of (CH ₃ COO) ₂ .2H ₂ O) for 10 minutes while stirring with ultrasonic waves, the graphite was suction-filtered, and then subjected to a heat treatment at 300 ° C. in air, and zinc acetate was applied to the surface thereof. Was provided, followed by heating in a reducing atmosphere.

Thereafter, the carbon on which the metal oxide layer mainly composed of zinc acetate was formed was converted to an aqueous ruthenium chloride solution (300
mg / l Ruthenium chloride aqueous solution is adjusted to pH 5 with hydrochloric acid)
Immersion for 1 minute to deposit ruthenium on the surface.

After the electrode was formed in the same manner as in Example 1 using the catalyst, a fuel cell was prepared, and its characteristics were examined. As a result, the characteristics were exactly the same as those in Example 1.

Example 5 An electrode was prepared in the same manner as in Example 1 except that the catalyst to be supported was changed from platinum to an iridium catalyst, and a fuel cell was constructed.

The loading of the iridium catalyst depends on the supported catalyst.
250m specific surface area^Two/ G of graphite
The graphite was treated with 1 mol / l of zinc acetate (Zn).
(CH _ThreeCOO)_Two・ 2H_TwoO) supersonic in ethanol solution
After immersing for 10 minutes while stirring with waves, absorb the graphite.
After filtration, heat treatment is performed at 300 ° C in air.
A layer mainly composed of zinc acetate on the surface of
Heated in a neutral atmosphere.

Thereafter, the carbon on which the metal oxide layer mainly composed of zinc acetate was formed was converted to an aqueous iridium chloride solution (250
(1 mg / l iridium chloride aqueous solution was adjusted to pH 5 with hydrochloric acid) for 1 minute to precipitate iridium on the surface.

After the electrode was formed in the same manner as in Example 1 using the catalyst, a fuel cell was prepared and its characteristics were examined. As a result, the characteristics were exactly the same as those in Example 1.

(Example 6) An electrode was prepared in exactly the same manner as in Example 1 except that the supported catalyst was changed from platinum to a platinum / rhodium catalyst, and a fuel cell was constructed.

For supporting the platinum / rhodium catalyst, graphite having a specific surface area of 250 m ² / g was used as the carbon to be supported, and the graphite was mixed with 1 mol / l of zinc acetate (Z
After immersing in an ethanol solution of n (CH ₃ COO) ₂ .2H ₂ O) for 10 minutes while stirring with ultrasonic waves, the graphite was subjected to suction filtration, and then heat-treated at 300 ° C. in the air.
A layer mainly composed of zinc acetate was provided on the surface, and subsequently heated in a reducing atmosphere.

Thereafter, the carbon having a metal oxide layer mainly composed of zinc acetate formed thereon is mixed with a platinum chloride / rhodium chloride mixed aqueous solution (150 mg / l platinum chloride, 150 mg / l rhodium chloride mixed aqueous solution adjusted to pH 5 with hydrochloric acid). For 1 minute to precipitate a platinum / rhodium mixed catalyst on the surface.

After the electrode was formed in the same manner as in Example 1 using the catalyst, a fuel cell was prepared and its characteristics were examined. As a result, the characteristics were exactly the same as those in Example 1.

As described above, according to the catalyst supporting structure of the embodiment of the present invention, a catalyst having a large catalyst surface area and a high catalyst efficiency can be obtained without containing sulfur which causes deterioration with time, and an excellent fuel cell can be obtained. be able to.

[0041]

As described above, in the support structure of the present invention, the organic metal is applied to the surface of the support substrate, and then the heat treatment is performed in a non-oxidizing atmosphere, whereby the water repellency of the surface is improved. Even if the catalyst deposition step is in an aqueous solution (chloride aqueous solution), the catalyst noble metal can be uniformly deposited not only on the surface of the support substrate but also on the fine pores present in the support substrate, and the surface area of the attached catalyst can be reduced. growing. As a result, when the present catalyst is applied to an electrode of a fuel cell, a fuel cell with excellent discharge performance can be obtained. Further, the deposited catalyst does not contain sulfur that is a catalyst poison, and therefore, the fuel cell is less deteriorated with time. Can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a catalyst forming process according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of an electrode configuration according to an embodiment of the present invention.

FIG. 3 is a schematic sectional view of a fuel cell according to one embodiment of the present invention.

FIG. 4 is a diagram showing characteristics of a fuel cell;

FIG. 5 is a diagram showing fuel cell life characteristics.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Catalyst support base material 2 Metal oxide layer 3 White metal layer

Continuation of the front page (56) References JP-A-58-166644 (JP, A) JP-A-60-82137 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4 / 86-4/98 B01J 21/00-38/74

Claims (4)

(57) [Claims] Claims: 1. A layer comprising at least one or more conductive metal oxides as a main component is formed on the surface of a conductive catalyst-carrying substrate,
An electrode catalyst supporting structure characterized in that a white metal is adhered to this. 2. The electrode catalyst supporting structure according to claim 1, wherein the layer mainly composed of a conductive metal oxide is formed by a thermal decomposition method. 3. An electrode for a fuel cell, wherein the electrode catalyst supporting structure according to claim 1 is used. 4. A fuel cell comprising the fuel cell electrode according to claim 3.