JP2002093425A - Catalyst for air cell and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst producing an electrode which generates improved maintaining voltage with a large current of order of 10 mA/cm2, by improving MnOx (x=4/3 to 8/5). SOLUTION: As the catalyst, MnOx (x=4/3 to 8/5) having an average particle size <=100 nm, obtained by thermally treating a complete solid solution of γ-Mn2O3 and γ-Mn3O4 in ultrafine particle synthesized by a solution method is used. A water solution of manganese salt and an excessive alkaline water solution are reacted to obtain a manganese hydroxide suspension, which is heated at 40 to 80 deg.C, and manganese ions are oxidized by blowing air into the suspension. Thus, the complete solid solution of γ-Mn2O3 and γ-Mn3O4 in ultrafine particles having an average particle size <=100 nm. Then, this complete solid solution is thermally treated at 350 to 500 deg.C to obtain manganese oxide represented in a formula MnOx (x=4/3 to 8/5) in ultrafine particles having average particle size <= primary particle 100 nm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air electrode used for an air (oxygen) fuel cell, a button type air cell, and the like, and a method for producing a catalyst thereof.

[0002]

2. Description of the Related Art Conventionally, various catalyst materials for air batteries have been studied. Numerous studies have been conducted on such materials as precious metals such as platinum group elements and silver deposited on activated carbon or carbon black, mixtures of activated carbon and metal oxides, and mixtures of metal phthalocyanine and carbon powder or heat-treated products thereof. ing. In general, the catalytic effect of platinum group elements and silver is large, but in primary batteries such as button-type air batteries, it is difficult to recycle the air electrode, so the precious metal catalysts described above are very expensive. Become. For this reason, manganese oxide has been tried as one of the inexpensive catalysts in the past. Above all, 3-6
As seen in 9145, Mn ₅ O ₈ has been put to practical use as a relatively excellent manganese oxide catalyst.

[0003]

The Mn ₅ O ₈ catalyst takes the form of a mixed crystal of Mn ₃ O _{4 and the} like, which is unlikely to exist in a single composition, and has a MnO _x (x = 4/3 to 8/5). expressed.
This manganese catalyst is generally used in a mixture with activated carbon and a water-repellent material. This MnO _x (x = 4 /
3-8 / 5) An electrode using a catalyst has a drawable current of 1
It is as large as 0 mA / cm ² . However, the polarization is large, and the maintenance voltage is lowered, so that it has not always been satisfactory as a power source of a recent high-performance electronic device. An object of the present invention is to provide a catalyst which improves MnO _x (x = 4/3 to 8/5) and further provides an electrode having an improved maintenance voltage at a large current of the order of 10 mA / cm ^2. .

[0004]

Means for Solving the Problems The present invention is directed to an ultrafine particulate γ-Mn ₂ O ₃ and γ-Mn ₃ O ₄ solid solution synthesized by a solution method, the average particle diameter of which is 100 nm.
The following MnO _x (x = 4/3 to 8/5) is used as a catalyst. That is, the catalyst for an air battery of the present invention mainly comprises a manganese oxide represented by the formula MnO _x (x = 4/3 to 8/5), and the primary particles have an average particle size of 1
It is characterized by being ultrafine particles of not more than 00 nm. The ultrafine manganese oxide is preferably supported on carbon particles such as activated carbon or acetylene black.

The method for producing a catalyst for an air battery according to the present invention comprises the steps of:
-Mn ₂ O ₃ and γ-Mn ₃ O ₄ at 350-50
By heat treatment at a temperature of 0 ° C., predominantly manganese oxide MnO _x represented by the formula _{Mn 5 O 8 (x = 4} / 3~8 /
5), wherein a step of obtaining ultrafine particles having an average primary particle diameter of 100 nm or less is provided. Here, the atmosphere for the heat treatment is preferably an air or oxygen atmosphere. Γ-Mn ₂ O ₃ and γ-Mn
The total solid solution of ₃ O ₄ is obtained by reacting an aqueous solution of a manganese salt with an excess of an aqueous alkali solution to obtain a manganese hydroxide suspension;
° C, and air was blown into the suspension to oxidize manganese ions.
It can be obtained as the following ultrafine particles. The MnO _x (x = 4) of the present invention thus obtained.
/ 3-8 / 5) is immediately after preparation are principal Mn ₅ O _8, when left infiltrating alkali solution, Mn ₃
There may be a significant shift to O ₄ .

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Mn ₅ O ₈ itself is
No. 145, which is publicly known. According to the conventional manufacturing method, the shape of the obtained Mn ₅ O ₈ is acicular, short diameter,
Both major diameters were on the order of μm, and there were no ultrafine particles on the order of nm. MnO _{x of the} present invention
(X = 4/3 to 8/5), as shown in FIG.
(Transmission electron microscope) In photographing, a granular shape is observed,
The size of the primary particles has an average particle size of less than 50 nm, and is 100 nm or less even when variations are considered. Further, the specific surface area is as large as 30 m ² / g or more on average, and is 20 m ² / g or more even when variations are considered. It is sometimes said that the ultra-fine particles of the order of nanometers change the essential characteristics of the ultrafine particles.
The specific surface area of O _x (x = 4/3 to 8/5) can be greatly improved, and the catalytic action can be efficiently exhibited. Further, the size of the activated carbon used in combination is usually as large as several μm to several hundred μm, so that MnO _x (x = 4/3 to 8 /
5) can be carried. According to such a method, MnO _{x having} almost no conductivity (x = 4 / 3−
Even in the case of (8/5), since a considerable part is in contact with the activated carbon, the conductivity becomes good, and the catalytic effect can be further brought out. Thus, MnO _x (x = 4 / 3-
In the state where the activated carbon particles carrying 8/5) are kneaded with the fluororesin particles to form an electrode, a dense solid-liquid-gas three-phase interface is easily formed, and the entire electrode plate has a catalytic function. It can be used effectively.

As specific electrochemical characteristics, a large increase in the number of catalytic active sites makes it easier to extract a large current.
Conventionally, only 10 mA / cm ² could be taken out, but it can be taken out in the order of several tens mA / cm ² . Further, the sustain voltage can be improved even with a discharge of several mA / cm ² . In a button-type zinc-air battery, a small hole is usually formed in the positive electrode case, and air is taken into the battery from the hole. Oxygen in the air taken into the battery is ionized by the catalyst of the air electrode and converted into energy. In this type of air battery, the air intake is closed by a seal paper until it is normally used so that air does not flow into the battery. In such a sealed state, the catalyst is not activated and the voltage is as low as 1 V or less. Then, by peeling off the seal paper, air flows in, and the catalyst is activated, so that the battery voltage also increases.
It reaches the 4V level. It can be used only when the battery voltage is around 1.4V. Thus, the speed at which the battery voltage reaches the predetermined value is a problem, and the faster the better, the better. According to the catalyst of the present invention, it was also found that the rising speed of the voltage can be increased by increasing the active points.

The ultrafine MnO _x (x = 4 /
As a method for producing 3-8 / 5), first, a manganese hydroxide suspension is obtained by reacting an aqueous solution of a manganese salt with an excess aqueous alkali solution. Next, the manganese hydroxide suspension is heated to 40 to 80 ° C., and air is blown into the suspension to oxidize manganese ions, and to obtain ultrafine γ-particles having an average particle diameter of 100 nm or less. Mn ₂ O ₃ and γ
Obtaining a complete solid solution of -mn ₃ O _4. If the temperature at which the manganese hydroxide suspension is heated is lower than 40 ° C., other compounds and large particles are generated, and the particles do not become ultrafine particles.
When the heating temperature exceeds 80 ° C., other compounds are formed. Next, the solid solution obtained above is heat-treated at a temperature of 350 to 500 ° C. in an oxygen atmosphere or an air atmosphere to form ultrafine MnO _x (x =
4/3 to 8/5) can be obtained. The heat treatment time may be about 1 hour, but is preferably 2 hours or more. However, the effect does not change even if the heat treatment is performed for a long time.

As the manganese salt used here, manganese sulfate, manganese chloride, manganese nitrate or the like can be used. As the alkaline aqueous solution, an aqueous solution of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, or the like can be used. As described above, ultrafine γ-Mn ₂ O ₃ by the hydrothermal method is used.
Of a total solid solution of γ-Mn ₃ O ₄ and γ-Mn ₂
Only by appropriate heat treatment of a solid solution of the total percentage of O ₃ and γ-Mn ₃ O ₄ , MnO _x (x = 4/3 to 8 /
5) is generated. There is no such generation method so far,
This has been clarified for the first time by the present inventors. In addition,
Regarding the identification of MnO _x (x = 4/3 to 8/5) of the present invention, its characteristics can be confirmed by an X-ray diffraction image and a transmission electron micrograph as in Japanese Patent Publication No. 3-69145. .

[0010]

Embodiments of the present invention will be described below. Example 1 First, an excess aqueous solution of sodium hydroxide was added to an aqueous solution of manganese sulfate, and the mixture was aged sufficiently to obtain an alkaline manganese hydroxide suspension. This is heated to 50 ± 5 ° C., and air is further blown into the suspension to oxidize manganese ions, thereby forming a solid solution of ultrafine particles of γ-Mn ₂ O ₃ and γ-Mn ₃ O _4. Was synthesized. Then, after washing and drying, heat treatment was performed at a high temperature of 430 ° C. in an oxygen atmosphere for 5 hours to obtain ultrafine MnO _x (x = 4/3 to 8/5) of the present invention. . FIG. 1 shows the ultrafine MnO obtained as described above.
_x (x = 4/3 to 8/5) transmission electron micrograph (T
EM). It can be clearly seen that the size of the primary particles is distributed at 30 to 50 nm.

The MnO _x (x = 4/3 to 8/5) 3
0 parts by weight, activated carbon 20 parts by weight, carbon black 20
Parts by weight and 30 parts by weight of an aqueous dispersion of polytetrafluoroethylene as a solid content were mixed and kneaded with stirring. This is made of a metal nickel wire having a diameter of 0.1 mm.
The resultant was filled in a mesh screen to obtain a catalyst sheet having a thickness of 0.3 mm. This was heat-treated at 300 ° C. for 30 minutes to sinter the polytetrafluoroethylene to enhance the water repellency.
This catalyst sheet was punched into a disk having a diameter of 22.6 mm to form a catalyst layer. However, the diameter of the catalyst layer that works effectively in this case is 20 mm. A water-repellent film 2 made of a porous polytetrafluoroethylene film having the same size and a thickness of 0.2 mm was attached to one surface of the catalyst layer 1 to form an air electrode 3.

FIG. 2 is a view showing a 23.degree.
1 shows a button-type zinc-air battery with a height of 0 mm and a height of 3.0 mm. At the bottom of a nickel-plated steel case 6 also serving as a positive electrode terminal, a nonwoven fabric 9 made of polyvinyl alcohol-based synthetic fiber, an air electrode 3 and a microporous separator 5 are inserted. On the other hand, a sealing plate 7 also serving as a negative electrode terminal in which a gasket 8 is combined with a peripheral edge is filled with a negative electrode 4 mainly composed of zinc powder, and this is combined with the case described above. The sealed battery is formed by bending the battery. In addition,
An aqueous solution of potassium hydroxide was used as an electrolyte. The air intake hole 6 a provided at the bottom of the case 6 is sealed with a seal paper 10 attached to the bottom of the case 6. This battery is designated as A.

Example 2 Using a powder processing machine (Mechano-Fusion System AMS manufactured by Hosokawa Micron Co., Ltd.), the same ultrafine MnO _x (x = 4/3 to 8 /) as in Example 1 was used.
5) was coated on the surface of the activated carbon particles. FIG. 3 shows MnO
_The activated carbon particles coated with _x (x = 4/3 to 8/5) are schematically shown. The size of the activated carbon particles 11 is on the order of several μm, and the coated MnO _x (x = 4/3 to 8/5) 12
The thickness of the layer was several hundreds to 300 nm. A battery B was produced in the same manner as in Example 1 except that this catalyst was used.

<< Comparative Example >> For comparison, a minor axis of 1-3 μm obtained by heat-treating γ-MnOOH in a nitrogen atmosphere at 400 ° C.
A battery was fabricated Z except for using the needle-like Mn ₅ O ₈ major axis 5~15μm in the same manner as in Example 1.

With respect to these batteries, a continuous constant current discharge test was performed by setting a discharge current value so as to be 5 mA / cm ² and 10 mA / cm ² with respect to the effective area of the catalyst. One hour after the discharge, the sustain voltage was compared. The results are shown in Table 1. The batteries A and B of the present invention have a significantly higher maintenance voltage than the battery Z of the comparative example. In particular, battery B has a high maintenance voltage. When compared with batteries, other factors also influence, so that differences in electrodes are generally less likely to appear. Comparing the model cell with a single pole of the air electrode,
It is likely that there will be a marked difference.

[0016]

[Table 1]

Next, the rising speed of the voltage when the seal paper was peeled was compared. The result is shown in FIG. FIG.
As is clear from the above, the battery of the present invention has a much faster voltage rise than the comparative example. In particular, the battery B is fast. This is presumably because the active sites of the catalyst have been significantly increased as compared with the conventional case.

In the above embodiment, MnO _x (x =
As materials for synthesizing 4/3 to 8/5), only one kind of each of the manganese salt and the alkaline aqueous solution is shown, but it is not necessarily limited to these, and other materials mentioned above may be used. it can. Further, γ-Mn ₂ O ₃ and γ-
The heat treatment temperature of the solid solution of Mn ₃ O ₄ is not limited to 430 ° C., but can be changed in the range of 350 ° C. to 500 ° C. To support MnO _x (x = 4/3 to 8/5) on activated carbon, almost all surfaces of activated carbon particles were coated with MnO _x (x = 4/3 to 8/5) by the mechanofusion method. For example, by using a surfactant or the like to increase the surface affinity between particles, MnO _x (x = 4/3 to 8/5)
Can be supported by coating activated carbon particles.

[0019]

As described above, according to the present invention, by using ultrafine MnO _x (x = 4/3 to 8/5) as a catalyst, a button-type air zinc battery excellent in large current characteristics can be obtained. Can be provided. The catalyst of the present invention is applicable not only to button-type zinc-air batteries but also to all electrochemical cells having an air electrode such as fuel cells.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of ultrafine MnO _x (x =
4/3 to 8/5) shows a transmission electron micrograph.

FIG. 2 is a vertical sectional view of a button-type zinc-air battery according to an embodiment of the present invention.

FIG. 3 shows an example of ultrafine MnO _x in an embodiment of the present invention.
It is a model figure showing typically a section of activated carbon particles which covered (x = 4 / 3-8 / 5).

FIG. 4 is a diagram comparing the voltage rise characteristics of the air battery when the seal paper is peeled off.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Catalyst layer 2 Water-repellent film 3 Air electrode 4 Negative electrode 5 Separator 6 Case 6a Air intake hole 7 Sealing plate 8 Gasket 9 Water-absorbing paper 10 Seal paper 11 Activated carbon particles 12 Ultrafine particles MnO _x (x = 4/3 to 8 / 5)

 ──────────────────────────────────────────────────の Continuing on the front page (72) Kenichi Nakatsu 1006 Kadoma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Tatsuya Nakamura 1-4-4 Meijishinkai, Otake City, Hiroshima Prefecture Toda Kogyo Inside the company creation center (72) Inventor Mitsuaki Hataya 1-1-1, Shinoki, Onoda-shi, Yamaguchi Prefecture Toda Kogyo Co., Ltd. Onoda Development Center F-term (reference) HH08 5H032 AA01 AS03 AS12 BB02 BB06 BB07 CC13 EE01 EE02 EE03 EE15 EE20 HH04 HH06

Claims (7)

[Claims] 1. Mainly of the formula MnO _x (x = 4/3 to 8/5)
Wherein the average particle size of primary particles of the manganese oxide is ultrafine particles of 100 nm or less. 2. The catalyst for an air battery according to claim 1, wherein the manganese oxide in ultrafine particles is supported on activated carbon or carbon particles. 3. A heat treatment of a solid solution of γ-Mn ₂ O ₃ and γ-Mn ₃ O ₄ at a temperature of 350 to 500 ° C.
It is mainly composed of a manganese oxide represented by the formula MnO _x (x = 4/3 to 8/5), and its primary particles have an average particle diameter of 100.
A method for producing a catalyst for an air battery, comprising a step of obtaining ultrafine particles having a diameter of not more than nm. 4. The method for producing an air battery catalyst according to claim 3, wherein the atmosphere for the heat treatment is an air or oxygen atmosphere. 5. A step of reacting an aqueous solution of a manganese salt with an excess aqueous alkali solution to obtain a manganese hydroxide suspension, and heating the obtained manganese hydroxide suspension to 40 to 80 ° C. _4. A step of blowing air into the liquid to oxidize manganese ions to obtain an ultrafine γ-Mn ₂ O ₃ and γ-Mn ₃ O ₄ solid solution having an average particle diameter of 100 nm or less. Of producing a catalyst for an air battery. 6. The method for producing a catalyst for an air battery according to claim 5, wherein the manganese salt is selected from the group consisting of manganese sulfate, manganese chloride, and manganese nitrate. 7. The method according to claim 5, wherein the aqueous alkaline solution is an aqueous solution of at least one compound selected from the group consisting of sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate.