JPS5948511B2 - Electrodes for fuel cells and air cells - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides electrodes for fuel cells and air cells that have small polarization and can obtain large currents, more specifically, an air electrode or an oxygen electrode for fuel cells and air cells. The present invention relates to the novel above-mentioned electrode, wherein the electrode contains cyanocobalamin (vitamin B, . . . ) as a catalyst.

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

That is, the air electrode catalyst or oxygen electrode catalyst for fuel cells may be doped with metals such as copper, silver, gold, platinum, palladium, or osmium, or iron or copper phthalocyanine, tungsten bronze, or activated carbon or lithium. nickel oxide, etc., and noble metals such as platinum, palladium, ruthenium, silver, etc. as air electrode catalysts for air batteries.
Alloys such as Ag-Hg and Ru-Au, or transition metal oxides such as manganese and osmium, as well as NiFe, O,
CoFe20.

, spinel oxides such as 304 and CoA1204 have been proposed for Ni0. However, among these catalysts in the prior art, precious metals are expensive and uneconomical;
On the other hand, although non-precious metals are inexpensive, air electrodes or oxygen electrodes using them as catalysts suffer from considerable polarization, and electrode characteristics such as a considerable potential drop in high current density regions are unavoidable. is not sufficient, and in turn,
Fuel cells and air cells incorporating such electrodes have the drawback of not being able to obtain large currents.

The present invention has been made in view of the above-mentioned current situation, and its purpose is to have small polarization and to be able to obtain a large current with almost no potential drop even in a large current density region. It is an object of the present invention to provide an air electrode or an oxygen electrode used in energy-dense fuel cells and air cells.

The present invention, which achieves this object, is an electrode for fuel cells and air cells, characterized in that the air electrode or oxygen electrode of the fuel cell and air cell contains cyanocobalamin (vitamin B12).

F. Until now, there has been no example of using cyanocobalamin as a catalyst in the air electrode or oxygen electrode for fuel cells and air cells.

According to the present invention, a novel configuration in which the electrode contains cyanocobalamin reduces polarization, as will be described later.
Moreover, the excellent effect of making it possible to obtain a large current can be obtained. The air electrode or oxygen electrode containing cyanocobalamin according to the present invention is used by incorporating it into a fuel cell or an air cell (metal air cell) as a positive electrode.

A fuel cell uses hydrogen gas etc. as a negative electrode active material, and an alkaline electrolyte such as KOH or NaOH, or NaC as an electrolyte.
The air battery is constructed using a neutral electrolyte such as 1, KCl, etc., and an acidic electrolyte such as phosphoric acid, and the air battery uses zinc, aluminum, magnesium, platinum, or an alloy thereof as the negative electrode active material, and the above-mentioned electrolyte is used as the negative electrode active material. Constructed using the same thing as . The electrode material of the air electrode or oxygen electrode in the present invention is made of a mixed powder of a carbon material such as carbon powder, activated carbon, graphite, or acetylene black, and a water repellent such as Teflon, and cyanocobalamin is mixed therein. Or supported by means such as impregnation. The electrode is fabricated by molding and pressing a mixed powder consisting of the above-mentioned carbon material, water repellent, cyanocobalamin, etc. together with a metal mesh of nickel, silver, etc., followed by heating and baking, and its structure is as shown in FIG. The electrode of the present invention produced in this way is installed in a fuel cell or an air cell by arranging the electrode material so that it is in contact with the electrolyte side and the metal mesh with the gas side. Example 1 below
As shown in FIG. 1, 1 is an electrode material layer and 2 is a metal mesh. Then, in order to extend the life of the electrode, a second layer of electrode material may be provided in a sandwich shape on the outside of the metal mesh in contact with the gas side, in which case the second layer covers the first layer on the electrolyte/electrolyte side. The mixing ratio of water repellent agent is higher than that of the layer to increase water repellency and increase porosity.

The amount of cyanocobalamin used may be within the catalytic amount that achieves the object of the present invention, and it can also be used in combination with other catalysts. In addition, the electrode of the present invention. Other materials may be appropriately added as long as they do not contradict the purpose. The reason why cyanocobalamin is effective as a catalyst is that in the metal complex j part where cobalt is present as a coordination center metal at the center of a ring with a planar structure similar to a porphyrin ring, the 3d orbital electron of cobalt and the antibonding property π of the oxygen molecule This is thought to be because oxygen molecules are easily adsorbed to the metal complex portion due to interaction with electrons, and this interaction further lowers the reaction energy of oxygen molecules and increases the electrochemical reaction rate.

Next, the present invention will be explained with reference to Examples, but the present invention is not limited thereto in any way.

In addition, in the following examples, measurements were performed at room temperature of 20 to 25°C. Example 1 Carbon powder (passed through 100 meshes) 0.20g, activated carbon 0
．． 08g, Teflon powder (passed through 50 meshes) 0.12
g and 0.05 g of cyanocobalamin were mixed, and this was placed in a disk molding mold with a diameter of 20 mm together with 50 meshes of nickel mesh, and the pressure was 400 kg/? , then heated in a dryer at 130°C for 30 minutes, and then heated at 40°C for 30 minutes.
An electrode was produced by baking in a furnace at 0° C. for 30 minutes.

Figure ] shows the structure of this electrode, where ] is an electrode material layer made of the above-mentioned mixed powder, and 2 is a nickel mesh. When this 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 2 is in contact with the gas.
As a result, a three-phase interface of electrolyte, gas, and electrode particles is formed in the electrode material layer 1. A battery was produced using 1NKOH as the electrolyte and platinum as the negative electrode.

Then, the electrode potential (E/vs Ag
-AgCl) was measured. Figure 2 a
is the potential-current curve in air, and b is that in oxygen gas.

According to the measurement results shown in Figure 2, the equilibrium potential in air is -0.0
5V (vs. Ag-AgCl) at 100 mA/♂ is -0.338V (vs. Ag-AgCl), and in oxygen gas the equilibrium potential is -0.038V (vs. Ag-AgCl)
0.31V at 100mA/An2 (vs. Ag
-AgCl). Example 2 Activated carbon is added to a 1% by weight ethanol solution of cyanocobalamin to impregnate the activated carbon with cyanocobalamin, and then dried.

To 0.08 g of this activated carbon, 0.20 g of carbon powder (passed through 100 meshes) and 0.20 g of Teflon powder (passed through 50 meshes).
Example 1
Electrodes were prepared in the same manner as above, and a battery was constructed. FIG. 3a shows the potential-current curve of the electrode in Example 2.

For reference, b in the figure shows a potential-current curve of an electrode prepared in the same manner as in Example 2, except that conventional platinum nitrate was used instead of cyanocobalamin. According to the measurement results shown in Figure 3, the electrode of the present invention has smaller polarization than the conventional electrode using platinum nitrate, and is stable with no significant drop in potential even in the high current density region. I understand that.

As is clear from the above explanation, the electrode of the present invention using cyanocobalamin has small polarization and almost no potential drop even in the high current density region, and is superior to conventional products in this respect. It has the following effects.

For this reason, fuel cells and air cells incorporating this electrode as an air electrode or oxygen electrode can obtain large currents and have even higher energy density, which is extremely high compared to conventional products. Practical value can be expected.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of an electrode that is a specific example of the present invention, FIG. 2 is a potential-current curve of an electrode in Example 1 of the present invention, and FIG. 3 is a potential-current curve of an electrode in Example 2. A comparison between the curve and the potential-current curve of a conventional product using platinum nitrate is shown. In FIG. 1, 1... electrode material layer made of carbon powder, catalyst, etc., 2... nickel net.

Claims (1)

[Claims] 1. An electrode for fuel cells and air cells, characterized in that the air electrode or oxygen electrode of the fuel cell and air cell contains cyanocobalamin (vitamin B_1_2).