Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Patent
1984-11-19
1986-06-17
Hearn, Brian E.
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
429 40, 429224, H01M 400, H01M 486
Patent
active
045956430
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to improvements in catalysts for use in the air zinc cell, and is intended to provide an air zinc cell having excellent high-rate discharge characteristics and storage characteristics.
BACKGROUND ART
The cells to which the catalyst electrode of this invention are applicable include fuel cells using alkaline electrolytes, air zinc cells for stationary or installation use, etc. but is particularly useful for the air-zinc button cell.
The catalyst materials heretofore explored from very early times to the present day are various metals and metal oxides, activated carbon, carbon, etc. Thus, noble metals such as metals of the platinum group and silver as deposited on activated carbon or carbon black, mixtures of metal oxides with carbon, and mixtures of metal phthalocyanine complexes with carbon, whether heat-treated or not, may be mentioned by way of example.
Generally, noble metal elements represented by platinum and palladium have relatively high catalyst activity but when the difficulty of regeneration for reuse is taken into consideration, as it is important in the case of primary cells such as air-zinc button cells, noble metal catalysts have the disadvantage that they cannot be provided at low cost.
For the above reason, it has been attempted over years to explore the use of manganese oxide as an inexpensive catalyst for air cell use. For example, U.S. Pat. Nos. 3,948,684, 4,121,018 and 4,269,691 teach such catalysts. According to these patents, various types of chemical manganese are subjected to chemical or heat treatment so as to precipitate MnO.sub.2, Mn.sub.2 O.sub.3 or/and Mn.sub.3 O.sub.4 on carbon or mix .gamma.MnO.sub.2 with carbon and alkali to constitute a catalyst.
As pointed out in the aforementioned United States Patents, manganese oxides have catalyst activity and some of them have satisfactory discharge characteristics at a current not exceeding several mA/cm.sup.2 but these oxides are not necessarily fully satisfactory in high-rate discharge at a current of more than 10 mA/cm.sup.2 and in discharge characteristics after storage. Under the circumstances there has been demanded a manganese oxide having improved catalyst activity and storage stability.
DISCLOSURE OF THE INVENTION
This invention relates to a catalyst for an alkaline air cell, said catalyst comprising a manganese oxide obtainable by heat-treating .gamma.-manganese oxyhydroxide (.gamma.-MnOOH), particularly a manganese oxide obtainable by heat-treating .gamma.-MnOOH at a temperature between 250.degree. C. and 450.degree. C. and whose X-ray diffraction pattern is mainly characteristic of Mn.sub.5 O.sub.8.
The manganese oxyhydroxide .gamma.-MnOOH used for the practice of this invention occurs as acicular crystals as shown in FIG. 1, which crystals having a major-axis length a of not more than 10.mu. and a minor-axis length b of not more than 1.mu., with an aspect ratio a/b of <10.
This acicular crystalline configuration remains unchanged even after the heat treatment.
FIG. 2 shows the thermogravimetric weight-loss curves of .gamma.-MnOOH in various atmospheres. The inert atmospheres I of nitrogen, argon and helium gases and the air atmosphere II tend to show substantially the same course of weight change but in the temperature region indicated at b in FIG. 2, the weight changes in inert atmospheres I, i.e. nitrogen, argon and helium, are greater than in the air (II).
In regard to X-ray diffraction patterns, when the heat treatment in nitrogen, argon or helium is conducted at 250.degree. to 300.degree. C., Mn.sub.5 O.sub.8 is produced in a substantial proportion although some amount of .gamma.-MnOOH remains unreacted and a diffraction pattern characteristic of Mn.sub.5 O.sub.8 and, to a lesser extent, of Mn.sub.3 O.sub.4 is observed up to 450.degree. C. but an X-ray diffraction pattern characteristic of .alpha.-Mn.sub.2 O.sub.3 is obtained at 500.degree. C.
The heat treatment in air shows substantially the same tendency as that in nitrogen or argon but Mn.sub.5 O.sub.8 is predomina
REFERENCES:
patent: 4121018 (1978-10-01), Kocherginsky et al.
patent: 4269691 (1981-05-01), Deborski
patent: 4405699 (1983-09-01), Kruger
Hayakawa Hayashi
Koshiba Nobuharu
Momose Keigo
Ohta Akira
Hearn Brian E.
Kalafut S. J.
Matsushita Electrical Industrial Co. Ltd.
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