JPH0119628B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an electrode for a fuel cell or an air cell that has small polarization and can obtain a large current, and more specifically, an air electrode or an oxygen electrode for a fuel cell or an air cell. The present invention relates to the above novel electrode, wherein the electrode contains both iron phthalocyanine and cobalt vanadate CO ₂ V ₂ O ₇ as catalysts.

Conventionally, various proposals have been made regarding catalysts used in air electrodes or oxygen electrodes for fuel cells and air cells.

That is, as air electrode catalysts or oxygen electrode catalysts for fuel cells, metals such as copper, silver, gold, platinum, and palladium, tungsten bronze, iron or copper phthalocyanine, activated carbon, and nickel oxide doped with lithium are known. In addition, as air electrode catalysts for air batteries, noble metals such as platinum, palladium, rutinium and silver, alloys of silver and mercury and rutinium and gold, oxides of transition metals such as manganese and osmium, and _{NiFe2O4 , CoFe2O4 , NiCr2O4 _}
Spinel oxides such as CoAl 2 O ₄ and CoAl ₂ O 4 are known.

However, among these catalysts in the prior art, noble metals are expensive and therefore uneconomical, while others are inexpensive, but the air electrode or oxygen electrode using these as catalysts has a polarization greater than that of noble metals. In addition, the electrode characteristics are not sufficiently good, such as a considerable potential drop in the high current density region being unavoidable, and as a result, large currents cannot be obtained in fuel cells and air cells incorporating such electrodes. There was a drawback.

The present invention has been made in view of the current situation, and its purpose is to provide a high energy density device with small polarization, almost no potential drop even in a high current density region, and a high current that can be obtained. The present invention provides electrodes for fuel cells and air cells.

To summarize the present invention, the electrode for fuel cells and air cells of the present invention is characterized in that the positive electrode contains iron phthalocyanine and cobalt vanadate as a catalyst.

Until now, there has been no example of using both iron phthalocyanine and cobalt vanadate as catalysts in air electrodes or oxygen electrodes for fuel cells and air cells. According to the present invention, a novel configuration in which the electrode contains both iron phthalocyanine and cobalt vanadate makes it possible to reduce polarization and obtain a large current compared to when each is used alone, as described below. Excellent combined effects can be obtained.

The present invention will be explained in more detail.

A fuel cell is constructed by using hydrogen gas as a negative electrode active material, alkaline electrolytes such as KOH and NaOH, neutral electrolytes such as NaCl and KCl, and acidic electrolytes such as phosphoric acid as electrolytes. Batteries use zinc, aluminum, magnesium, platinum, or alloys of these as negative electrode active materials,
It is constructed using the same electrolyte as above.

The electrode of the present invention is used as a positive electrode of the above-mentioned fuel cell or air cell, and the above-mentioned positive electrode material is a combination of a carbon material such as carbon powder, activated carbon, graphite, or acetylene black, and a water repellent agent such as Teflon. It consists of a mixed powder, and according to the present invention, a mixed substance of iron phthalocyanine and cobalt vanadate is supported thereon as a catalyst by means such as mixing.

The positive electrode can be produced by molding and pressing a mixed powder consisting of the carbon material, water repellent, iron phthalocyanine, and cobalt vanadate together with a metal mesh of nickel, silver, etc., and then heating and baking the mixture.

The reason why the above-mentioned mixture of iron phthalocyanine and cobalt vanadate in the present invention is effective as a composite catalyst is that the most efficient four-electron reaction (O ₂ + 2H ₂ O + 4l ^- → 40H ^- ) can be selected among the positive electrode reactions. When the selectivity of the four-electron reaction with iron phthalocyanine is low (O ₂ +H ₂ O+2l ^- →HO ₂ ^-- +OH ^- ,
HO ₂ ^- → 1/20 ₂ +OH ^- two _- electron reaction is predominant) _.
This is thought to be because by supporting cobalt vanadate, which increases the decomposition rate of HO ₂ ^- ), it is easy to supply enough electrons to make the electrode reaction proceed smoothly no matter what reaction process is used. In particular, the results of the measurements show that the decomposition rate of the intermediate is
It is almost the same as platinum black, and twice as much as iron phthalocyanine alone.

The mixing ratio of iron phthalocyanine and cobalt vanadate is preferably 1 part iron phthalocyanine to 0.1 to 9 parts cobalt vanadate. If it is less than 0.1, the effect will be similar to that of iron phthalocyanine alone, while 9
This is because if it exceeds the above, the effect will be similar to that of cobalt vanadate alone, and the advantage of mixing both may be lost.

Next, the structure of the positive electrode in the present invention will be explained with reference to the drawings. That is, FIG. 1 shows a schematic cross-sectional view showing a specific example of the structure of the positive electrode (air electrode) according to the present invention, in which 1 shows an electrode material layer and 2 shows a nickel mesh.

When this air electrode is assembled into a battery, it is oriented so that the electrode material layer 1 is in contact with the electrolyte and the nickel mesh is in contact with the gas. As a result, electrode material layer 1
A three-phase interface of electrolyte, gas and electrode powder is formed therein. Note that the nickel net 2 has an electrode material layer 1
It is provided as a support and a current collector. In this case, in order to extend the life of the electrode, a second electrode material layer may be provided in a sanderch type on the outside of the metal mesh in contact with the gas side. In this case, the second electrode material layer The mixing ratio of the water repellent agent is higher than that of the first electrode material layer provided on the side to increase water repellency and increase porosity.

Next, the present invention will be explained with reference to Examples, but the present invention is not limited thereto in any way.
In addition, the measurement of the current dependence of the electrode potential in the Examples was carried out at room temperature of 20 to 25°C.

Example 1 4 g of carbon powder (passed through 200 meshes), 4 g of acetylene black, 0.2 g of a catalyst mixture of iron phthalocyanine and cobalt vanadate, and 3.3 g of Teflon emulsion (containing 60% Teflon) were mixed well and formed into a sheet using a roll. . After the sheet is dried in the air for about 30 minutes, a nickel mesh (50 mesh) is placed on one side and hot pressed at a temperature of 250°C and a pressure of 100 kg/cm ² for 30 minutes. Cooled in air, diameter 30mm
An air electrode (positive electrode) was prepared by cutting out a circular shape.
Cobalt vanadate was obtained by calcining a predetermined amount (2:1) of CoO and V ₂ O ₅ at 690° C. for 24 hours in air. An air battery was constructed using IN KOH as the electrolyte and zinc as the negative electrode, and the dependence of the electrode potential (E, vs. saturated calomel electrode) of the air electrode in air on current density was investigated. The results are shown in Figure 2. That is, FIG. 2 is a graph showing the relationship between the current density of the air electrode and the electrode voltage in this example,
In this example, A is when the weight ratio of the mixed catalyst is iron phthalocyanine 1:1 cobalt vanadate,
In this example, B is C when the weight ratio of the mixed catalyst is iron phthalocyanine 4:1 cobalt vanadate.
In this example, the ratio is iron phthalocyanine 1:4.
In the case of cobalt vanadate, D and E are the air electrodes using a conventionally known catalyst, D is the case where iron phthalocyanine is used, and E is the case where a silver catalyst is used.

According to Figure 2, when iron phthalocyanine and cobalt vanadate are mixed and supported at a weight ratio of 1:1, the equilibrium potential is +0.014V (vs. SCE <<saturated calomel electrode>>) and -0.61 at 100mA/ ^cm2 . (vs. SCE), On the other hand, when iron phthalocyanine and cobalt vanadate are mixed and supported at a weight ratio of 4:1, the equilibrium potential is +0.024 V (vs. SCE), and - at 100 mA/cm ²
It becomes 0.061V (vs. SCE).

As is clear from Figure 2, compared to the conventional case using iron phthalocyanine and silver, the equilibrium potential is higher and the polarization is smaller in the case of the present invention using a mixture of iron phthalocyanine and cobalt vanadate. , and is stable with no significant drop in potential even in the high current density region.

As explained above, the positive electrode (air electrode or oxygen electrode) in the present invention supports a mixture of iron phthalocyanine and cobalt vanadate as catalysts.
The polarization is small, and there is almost no potential drop even in the high current density region, and in this respect, it exhibits superior effects compared to conventional ones. Therefore, fuel cells and air cells incorporating this electrode as a positive electrode can obtain large currents and have even higher energy density, and are expected to have extremely high practical value compared to conventional products. be able to.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional schematic diagram showing a specific example of the structure of the positive electrode (air electrode) according to the present invention, and FIG. 2 is a graph showing the relationship between current density and electrode potential of the air electrode of the embodiment of the present invention. It is. 1... Electrode material layer, 2... Nickel net.

Claims (1)

[Claims] 1. An electrode for a fuel cell or an air cell, which contains iron phthalocyanine, which is a transition metal complex, and cobalt vanadate, which is a composite metal oxide, as a catalyst.