JP2019172487A - Cobalt composite γ-type manganese dioxide and method for producing the same - Google Patents

Abstract

To provide a catalyst that has a high activity for oxygen evolution reaction, and, in particular, a method for increasing the catalytic activity for oxygen evolution reaction of manganese dioxide and a manganese dioxide that has a catalytic activity increased thereby.SOLUTION: Provided are: a cobalt composite γ-type manganese dioxide characterized by containing cobalt in the crystal structure; a catalyst for oxygen evolution reaction, comprising said cobalt composite γ-type manganese dioxide; and a method for producing a cobalt composite γ-type manganese dioxide characterized in that a solution in which a cobalt salt and a reducing agent are dissolved is brought into contact with γ-type manganese dioxide and then dried.SELECTED DRAWING: Figure 2

Description

  The present invention relates to cobalt composite γ-type manganese dioxide, an oxygen generation reaction catalyst including the same, an electrode material and an electrode, a secondary battery or an air battery including the electrode, and a method for producing cobalt composite γ-type manganese dioxide.

In recent years, hydrogen fuel that does not impact the environment has attracted attention as an alternative to fossil fuel. Water electrolysis is one of hydrogen sources, and generates hydrogen and oxygen as represented by the following formula (1).
(1) 2H ₂ O → 2H ₂ + O ₂
At this time, the hydrogen generation reaction of the following formula (2) occurs at the cathode, and the oxygen generation reaction of the following formula (3) occurs at the anode of the counter electrode.
(2) 2H ⁺ + 2e ⁻ → H ₂
(3) 2H ₂ O → O ₂ + 4e ⁻ + 4H ⁺
Since the oxygen generation reaction is thermodynamically disadvantageous and a slow four-electron reaction, water electrolysis is limited by this oxygen generation reaction. As the catalyst for accelerating the oxygen generation reaction, oxides of ruthenium and iridium, which are noble metals, are particularly effective, but these are very rare and expensive and are not suitable for large-scale production. Therefore, development of a highly active oxygen generating catalyst using abundant resources at low cost has been desired.

Manganese dioxide (MnO ₂ ) is inexpensive and has abundant resources, and is safe and has a low environmental impact, as can be seen from its long history of use as a battery material. In addition, MnO ₂ takes a crystal structure such as α-, β-, γ-, δ-, R-, etc., by a combination of octahedral units in which six O atoms are coordinated to Mn atoms. Changes in physical properties. And γ-MnO ₂ is an irregular intergrowth of R- and β-MnO ₂ having 2 × 1, 1 × 1 tunnels, respectively, and this unique structure provides excellent electrochemical properties, and the battery It is a material suitable for applications. However, γ-MnO ₂ has not been used as an oxygen generating catalyst because of its extremely low catalytic activity for oxygen generating reaction. In order to improve the low catalytic activity of manganese dioxide with respect to the oxygen evolution reaction, a method of mixing a base or carbonate having a pKa of 8 or less with manganese dioxide has been proposed (Patent Document 1), but the object is α-MnO _2. And β-MnO ₂ , and the improvement effect was limited.

JP2015-192993A

  An object of the present invention is to solve these problems and provide a catalyst having a high activity for oxygen generation reaction, and particularly a method for enhancing the catalytic activity for oxygen generation reaction of manganese dioxide, which is abundant in resources, and this It is to provide manganese dioxide having a higher catalytic activity.

The inventors of the present invention have begun studying with the aim of developing a highly active oxygen-generating catalyst using inexpensive and abundant resources. In the study, the catalytic activity for oxygen evolution reaction is low among manganese dioxide, but the potential decrease in discharge is relatively slower than other types, so it is the most used as cathode material for primary battery, that is, long-term use as battery We considered whether or not γ-type manganese dioxide (γ-MnO ₂ ), whose safety is guaranteed by actual results, could be used. Then, when examination using γ-type manganese dioxide was advanced, a salt of cobalt such as cobalt chloride and a reducing agent such as hydrazine were added to a solvent such as water, and γ-MnO ₂ powder was immersed in this solution and stirred. As a result, it was found that cobalt (Co) and γ-MnO ₂ can be complexed, and the thus obtained γ-type manganese dioxide complexed with cobalt has a very high catalytic activity for the oxygen generation reaction. Further, the obtained γ-type manganese dioxide complexed with cobalt can be taken out by separating from the liquid in the solution by filtration or the like and then drying by vacuum drying or the like. The present invention has been completed in this way.

That is, the present invention is specified by the following items.
(1) A cobalt composite γ-type manganese dioxide containing cobalt in the crystal structure.
(2) A catalyst for oxygen generation reaction containing the cobalt composite γ-type manganese dioxide according to (1).
(3) A method for electrolyzing water, wherein the oxygen generation reaction catalyst described in (2) above is used as the oxygen generation reaction catalyst.
(4) An electrode containing the cobalt composite γ-type manganese dioxide described in (1) above in the material constituting the electrode.
(5) A secondary battery or an air battery comprising the electrode according to (4) above.
(6) A method for producing a cobalt composite γ-type manganese dioxide, wherein a solution in which a cobalt salt and a reducing agent are dissolved is brought into contact with γ-type manganese dioxide and then dried.
(7) including a step of immersing and stirring γ-type manganese dioxide particles in a solution in which a cobalt salt and a reducing agent are dissolved, and a step of filtering the solution in which the γ-type manganese dioxide particles are immersed and drying the residue. A process for producing a cobalt composite γ-type manganese dioxide as described in (6) above.
(8) The method for producing a cobalt composite γ-type manganese dioxide as described in (6) or (7) above, wherein the cobalt salt is cobalt chloride.
(9) The method for producing a cobalt composite γ-type manganese dioxide as described in any one of (6) to (8) above, wherein the reducing agent is hydrazine.
(10) A cobalt composite γ-type manganese dioxide obtained by bringing a solution in which a cobalt salt and a reducing agent are dissolved into contact with γ-type manganese dioxide and then drying.

  According to the present invention, by combining γ-type manganese dioxide with cobalt, it is possible to activate γ-type manganese dioxide that is inactive with respect to the oxygen generation reaction, and a cobalt composite having excellent activity with respect to the oxygen generation reaction. γ-type manganese dioxide can be provided, and a catalyst using the same can be provided. In addition, by using γ-type manganese dioxide complexed with cobalt according to the present invention, an electrode material, an electrode, a secondary battery, and an air battery excellent in battery characteristics can be provided.

Example 1, Comparative Example 1 and Comparative Example 2 is a view showing an XRD pattern of MnO ₂ that has been processed, respectively. ₂ is a diagram showing a linear sweep voltammogram of Co-γ-MnO ₂ obtained in Example 1 and untreated γ-MnO _2. FIG. It is a figure which shows the plot which used the common logarithm of the current density of FIG. 2 as a horizontal axis | shaft, and made the difference (overvoltage) with the standard electric potential of hydroxylation 1.23V the vertical axis | shaft. In Comparative Examples 1 and 2, a diagram illustrating a linear sweep voltammogram of MnO ₂ that has been processed, respectively. Co-γ-MnO ₂ obtained in Example 1, γ-MnO ₂ untreated illustrates a linear sweep voltammogram of commercial RuO ₂ and IrO _2. It is a figure which shows the plot which made the horizontal axis | shaft the common logarithm of the current density of FIG. 5 and made the vertical axis | shaft the difference (overvoltage) with the standard electric potential of 1.23V of hydroxylation. ₂ is a voltammogram showing the repetition characteristics of Co-γ-MnO ₂ obtained in Example 1. FIG. It shows a linear sweep voltammogram of the Co-γ-MnO ₂ obtained in Example 1 obtained in Example 2 Co-γ-MnO _2. And Co-γ-MnO ₂ obtained in Example 1, a diagram illustrating a linear sweep voltammogram of Co-γ-MnO ₂ obtained in Example 3. 6 is a diagram showing linear sweep voltammograms of Co-γ-MnO ₂ obtained in Example ₂ and Co-γ-MnO ₂ obtained in Example 4. FIG.

  The cobalt composite γ-type manganese dioxide of the present invention is characterized by containing cobalt in the crystal structure. The cobalt composite γ-type manganese dioxide of the present invention can be obtained by bringing a solution in which a cobalt salt and a reducing agent are dissolved into contact with γ-type manganese dioxide, followed by drying. The cobalt salt used in the production of the cobalt composite γ-type manganese dioxide of the present invention is not particularly limited as long as it is a cobalt salt, and examples thereof include hydrochloride, sulfate, nitrate, phosphate and the like. These hydrates may also be used. Of these, hydrochloride and sulfate are preferable, and hydrochloride is more preferable. Preferred examples of the hydrochloride include cobalt (II) chloride hexahydrate, and preferred examples of the sulfate include cobalt (II) sulfate heptahydrate. In the present invention, the cobalt salt includes a hydrate. The reducing agent used in the production of the cobalt composite γ-type manganese dioxide of the present invention is not particularly limited, and examples thereof include hydrazine, metal hydride, oxalic acid, and the like. Also good. Among these, hydrazine is preferable, and hydrazine in the present invention includes a hydrate. In the production of the cobalt composite γ-type manganese dioxide of the present invention, γ-type manganese dioxide is brought into contact with a solution in which the cobalt salt and the reducing agent are dissolved. The solvent for dissolving the cobalt salt and the reducing agent is not particularly limited as long as the cobalt salt and the reducing agent are dissolved, and a commonly used solvent can be used, but water is preferably exemplified. it can. The γ-type manganese dioxide used in the production of the cobalt composite γ-type manganese dioxide of the present invention is not particularly limited, and the production method of the γ-type manganese dioxide itself is not particularly limited. In addition, the shape is not particularly limited, but from the viewpoint of increasing the contact area with the solution and bringing it into uniform contact, the particle shape is preferable, and the average particle diameter is preferably several tens nm to several hundreds μm, and preferably 100 nm to 50 μm is more preferable. The purity is preferably 91 to 100% from the viewpoint of use as an oxygen generation reaction catalyst or electrode material. The particle size distribution of γ-type manganese dioxide can be measured by a laser diffraction particle size distribution measuring device.

  In the production of the cobalt composite γ-type manganese dioxide of the present invention, the cobalt salt and the reducing agent are dissolved in the solvent. The solution thus obtained is brought into contact with γ-type manganese dioxide. The method of bringing both into contact is not particularly limited, and a known method can be applied. For example, both can be brought into contact by immersing and stirring γ-type manganese dioxide particles in the solution. In addition, when the cobalt salt and the reducing agent are dissolved in a solvent, precipitation may occur. In this case, the γ-type manganese dioxide particles are immersed in the solution in which the precipitation has occurred and stirred together with the precipitation. The temperature at which the cobalt salt and the reducing agent are dissolved, and the temperature at which the γ-type manganese dioxide particles are immersed and stirred may be room temperature, but preferably 20 to 80 ° C., after the γ-type manganese dioxide particles are added. Stirring is preferably performed, for example, for 5 to 60 minutes until the manganese dioxide particles in the solution are uniformly dispersed. Thereafter, the liquid in the solution containing γ-type manganese dioxide particles is separated by a known method such as filtration. And the cobalt composite gamma-type manganese dioxide of this invention can be obtained by drying the obtained residue. Drying can be performed by a known method such as vacuum drying. The residue may be washed with distilled water or the like before drying. The ratio between the γ-type manganese dioxide immersed in the solution and the cobalt salt added to the solution is determined based on the molar ratio of the manganese atom and the cobalt atom in consideration of the ratio of the cobalt atom taken into the crystal structure of the γ-type manganese dioxide. In terms of the ratio, Mn: Co = 10: 1 to 2: 1 is preferable, and 8: 1 to 2: 1 is more preferable. The ratio of the γ-type manganese dioxide immersed in the solution and the reducing agent added to the solution is preferably 1 to 20% by mass, and 5 to 15% by mass of the reducing agent with respect to γ-type manganese dioxide. More preferably. The molar ratio of manganese atom to cobalt atom in the cobalt composite γ-type manganese dioxide of the present invention is not particularly limited as long as it has activity for oxygen generation reaction, but from the viewpoint of further improving activity for oxygen generation reaction, Mn : Co = 30: 1 to 10: 1 is preferable, and 20: 1 to 15: 1 is more preferable.

(Catalyst for oxygen generation reaction)
The cobalt composite γ-type manganese dioxide obtained as described above is very excellent in activity for oxygen generation reaction and can be used as a catalyst for oxygen generation reaction. The oxygen generation reaction catalyst is a catalyst used for the oxygen generation reaction. The oxygen generation reaction catalyst of the present invention is characterized by containing the cobalt composite γ-type manganese dioxide of the present invention, and may comprise only the cobalt composite γ-type manganese dioxide of the present invention, as long as the catalyst activity is not inhibited. May be included. The oxygen generation reaction catalyst of the present invention can be used, for example, as a catalyst on the oxygen generation reaction side in electrolysis of water. The water electrolysis method of the present invention is characterized in that the oxygen generation reaction catalyst of the present invention is used as an oxygen generation reaction catalyst. Since the catalyst for oxygen generation reaction of the present invention has high catalytic activity for the oxygen generation reaction, the electrolysis efficiency of water can be improved when it is disposed on the oxygen generation reaction side electrode. In the water electrolysis method of the present invention, as the catalyst on the hydrogen generation side, a known and commonly used catalyst can be used, and examples thereof include platinum and molybdenum disulfide. Moreover, what is normally used for electrolysis of water can be used for the other electrode material used for electrolysis of water, a power supply, a container, etc.

(Electrode, secondary battery or air battery)
The electrode of the present invention is characterized in that the material constituting the electrode contains the cobalt composite γ-type manganese dioxide of the present invention. The electrode of the present invention is not particularly limited as long as the material constituting the electrode contains the cobalt composite γ-type manganese dioxide of the present invention. For example, a conductive sheet, a conductive plate, or the like can be used to fix the cobalt composite γ-type manganese dioxide of the present invention to a current collector, and the cobalt composite γ-type manganese dioxide of the present invention can be used as a conductive agent such as acetylene black, What mixed with a binder, a solvent, etc. is apply | coated to an electroconductive sheet, an electroconductive board, etc., and it can dry and can form what formed the layer containing cobalt composite gamma-type manganese dioxide. The electrode of this invention can be used for the positive electrode of a secondary battery, and the air electrode side of an air battery. That is, the secondary battery or the air battery of the present invention includes the electrode of the present invention. In the secondary battery or the air battery of the present invention, materials and parts usually used in the secondary battery or the air battery other than the electrode of the present invention can be used. For example, normally used active materials, catalysts, Conductive agents, binders, electrolytes, electrodes, and the like can be used.

[Example 1]
(Preparation of Co-γ-MnO ₂ )
0.5 g of cobalt (II) chloride hexahydrate was dissolved in distilled water to make 10 mL. To this solution, 40 μL of hydrazine monohydrate was added and stirred for 5 minutes using a stir bar. At this time, a pale blue precipitate could be confirmed. To this solution, 0.5 g of γ-MnO ₂ powder (manufactured by Tosoh: HMR-AF, D ₅₀ = 16 μm) was added and stirred vigorously for 30 minutes. After stirring, the solution was filtered with suction, and the residue was rinsed with distilled water. The residue was collected and vacuum-dried at room temperature to complex cobalt with γ-MnO ₂ to obtain cobalt complex γ-type manganese dioxide (Co-γ-MnO ₂ ). The residue obtained by filtration did not show a pale blue precipitate with the naked eye and did not change even after drying. The ratio of manganese atom (Mn) to cobalt atom (Co) in the obtained cobalt composite γ-type manganese dioxide was determined using high frequency inductively coupled plasma optical emission spectrometry (ICP-AES) (SPS-3500, SII Nanotechnology Inc.). Measured. The result was Mn: Co = 19.6: 1.

[Comparative Example 1]
A sample treated with only the cobalt (II) chloride hexahydrate solution was prepared in the same manner as in Example 1 except that hydrazine monohydrate was not added.

[Comparative Example 2]
A sample treated with only the hydrazine monohydrate solution was prepared in the same manner as in Example 1 except that cobalt (II) chloride hexahydrate was not added.

(Structural analysis by X-ray diffraction)
The materials obtained in Example 1, Comparative Example 1 and Comparative Example 2 were each subjected to structural analysis using an X-ray diffractometer (Ultima-IV, Rigaku Corporation). The measured XRD pattern is shown in FIG. In FIG. 1, the top is the result of the used γ-MnO ₂ powder, (a) is the result of the sample prepared in Comparative Example 1, and (b) is the result of the sample prepared in Comparative Example 2. , (C) is the result of the substance obtained in Example 1. Pattern of MnO ₂ was treated only with the cobalt chloride solution (a) is the same as the pretreatment of gamma-MnO ₂ of the pattern, only cobalt chloride solution treatment was no change in the structure. In MnO ₂ (b) treated only with the hydrazine solution and the pattern (c) of the material obtained in Example 1, all the peaks were shifted to the low angle side. This indicates that the interatomic distance in MnO ₂ is increased while maintaining the structure. (B) and (c) have almost the same pattern and are considered to have the same structure.

(Linear sweep voltammetry: Example 1)
Linear sweep voltammetry of Co-γ-MnO ₂ obtained in Example 1 was performed. A three electrode cell was used, a platinum mesh was used as the reference electrode, and Ag / AgCl was used as the reference electrode. 5 mg of Co-γ-MnO ₂ obtained in Example 1 and 5 mg of acetylene black (conductive carbon) were added to a mixed solution containing 350 μL of ethanol, 350 μL of water and 95 μL of Nafion, and ultrasonically dispersed for 60 minutes. 78 μL of the obtained dispersion was dropped onto a disc electrode (diameter 5 mm) polished with alumina (amount of active material: 0.2 mg / cm ² ). Thereafter, the disk electrode was dried in air at room temperature, and this was used as a working electrode. As the electrolyte, 1M KOH purged with O ₂ for 30 minutes was used. The sweep speed was 1 mV / s, and the rotational speed was 1600 rpm in order to remove oxygen bubbles on the working electrode. Since the oxygen generation reaction involves proton generation, the hydroxylation potential changes depending on the pH of the electrolyte. The effect of pH can be canceled by converting to a reversible hydrogen electrode (RHE). The following formula was used for the conversion. The pH was 14.
E _RHE = 0.059 × pH + 0.199 + E _{Ag / AgCl}
Linear sweep voltammetry was similarly performed for untreated γ-MnO ₂ . FIG. 2 shows a linear sweep voltammogram. The dotted line in FIG. 2 is a result of only acetylene black not containing γ-MnO ₂ . As apparent from FIG. 2, the current response of acetylene black is very small, and the influence of acetylene black, which is a conductive carbon, can be ignored. Untreated commercial γ-MnO ₂ has a low current response and a low catalytic performance for oxygen evolution reaction. On the other hand, Co-γ-MnO ₂ subjected to the composite treatment showed a sharp rise in current, indicating that the performance of the catalyst for oxygen generation was greatly improved.

A Tafel plot was created for analysis of the rising portion of FIG. FIG. 3 shows a plot with the common logarithm of the current density of FIG. 2 as the horizontal axis and the difference (overvoltage) from the standard potential of hydroxylation of 1.23 V as the vertical axis. Table 1 shows the parameters calculated from FIGS. 2 and 3 (the start overvoltage is defined as the end point on the low potential side of the linear region in FIG. 3). The Tafel slope was calculated from the overlapping portion of the plot and the dotted line in FIG. 3 and approximated by the Tafel equation [η = a + blog (j)]. Here, a is a Tafel constant, b is a Tafel gradient, and j is a current density. The overvoltages of γ-MnO ₂ and Co-γ-MnO ₂ at 10 mA / cm ² were estimated to be 636 mV and 445 mV, respectively, and the Tafel slopes were estimated to be 87 mV / dec and 51 mV / dec, respectively. The Tafel slope is a potential difference required for the current value to be 10 times, and the smaller the value, the faster the reaction rate and the more active, and the faster the electron transfer in hydroxylation. γ-MnO ₂ shows a significantly faster reaction rate than γ-MnO ₂ .

(Linear sweep voltammetry: Comparative Examples 1 and 2)
Linear sweep voltammetry of the samples obtained in Comparative Examples 1 and 2 was performed in the same manner as in the case of Co-γ-MnO ₂ obtained in Example 1, respectively. The result is shown in FIG. For comparison, the results of Co-γ-MnO ₂ obtained in Example 1 measured above are also shown in FIG. The current response of both the sample obtained in Comparative Example 1 and the sample obtained in Comparative Example 2 is much smaller than that of Co-γ-MnO ₂ . From this, it can be seen that treatment with both hydrazine and cobalt is necessary to improve the current response.

From the above, the gamma-MnO ₂ treated only with hydrazine solution, gamma-MnO ₂ was treated with a solution containing both hydrazine and cobalt, the length of each side of the unit cell is increased. However, γ-MnO ₂ treated only with a hydrazine solution does not show catalytic activity because there is no cobalt. In addition, even when treated with a cobalt solution alone, γ-MnO ₂ does not show catalytic activity, which is probably because cobalt is simply attached to the surface of the γ-MnO ₂ particles or washed away with distilled water. . On the other hand, γ-MnO ₂ treated with a solution containing both hydrazine and cobalt increases the length of each side of the unit cell, and cobalt is contained in the crystal structure by substituting a part of the MnO ₂ skeleton. It is thought that there is.

(Linear sweep voltammetry: Comparison with precious metal catalysts)
In the case of Co-γ-MnO ₂ obtained in Example 1, linear sweep voltammetry of commercially available IrO ₂ (purity 99.9%, Strem Chemicals) and RuO ₂ (purity 99.9%, Sigma-Aldrich) As well as. The result is shown in FIG. The rising potential of the OER current was lowest for IrO _{2, and} was larger in the order of RuO ₂ , Co-γ-MnO ₂ obtained in Example 1, and γ-MnO ₂ . A Tafel plot was created for analysis of the rising portion of FIG. FIG. 6 shows a plot with the common logarithm of the current density in FIG. 5 as the horizontal axis and the difference (overvoltage) from the standard potential of hydroxylation at 1.23 V as the vertical axis. Table 2 shows the parameters calculated from FIGS. 5 and 6 (the start overvoltage is defined as the end point on the low potential side of the linear region in FIG. 6). The Tafel slope was calculated from the overlapping portion of the plot and the dotted line in FIG. 6 and approximated by the Tafel equation [η = a + blog (j)]. Here, a is a Tafel constant, b is a Tafel gradient, and j is a current density. The Tafel gradient was smallest in Co-γ-MnO ₂ (highest in catalytic activity), and increased in the order of IrO ₂ and RuO ₂ . The current on the noble side was much larger for Co-γ-MnO ₂ than for RuO ₂ .

(Repeatability evaluation)
The repetitive characteristics of Co-γ-MnO ₂ obtained in Example 1 were evaluated. Similarly to paragraph [0018], cyclic voltammetry of Co-γ-MnO ₂ obtained in Example 1 was performed. In this evaluation, 100 cycles were performed, and changes in characteristics due to repetition were measured. The result is shown in FIG.

[Example 2]
In place of 0.5 g of cobalt (II) chloride hexahydrate, 0.59 g of cobalt (II) sulfate heptahydrate (molar ratio of cobalt to manganese is the same as in Example 1) is the same as in Example 1. Cobalt composite γ-type manganese dioxide (Co-γ-MnO ₂ ) was prepared by the procedure. Unlike Example 1, immediately after the addition of hydrazine, the cobalt solution temporarily turned white, but immediately returned to the color immediately before the addition. Linear sweep voltammetry of Co-γ-MnO ₂ obtained in Example 2 was performed in the same manner as in Example 1. The result is shown in FIG. For comparison, the results of Co-γ-MnO ₂ measured in Example 1 are also shown in FIG. Co-γ-MnO ₂ obtained in Example 2 also showed an activity improving effect.

[Example 3]
Cobalt composite γ-type manganese dioxide (Co-γ-MnO ₂ ) was prepared in the same procedure as in Example 1 except that the addition amount of hydrazine monohydrate was changed to 20 μL and 80 μL, respectively. Linear sweep voltammetry of Co-γ-MnO ₂ obtained in Example 3 was performed in the same manner as in Example 1. The result is shown in FIG.

[Example 4]
Cobalt composite γ-type manganese dioxide (Co-γ-MnO ₂ ) was prepared in the same procedure as in Example 2 except that the addition amount of hydrazine monohydrate was changed to 20 μL and 80 μL, respectively. Linear sweep voltammetry of Co-γ-MnO ₂ obtained in Example 4 was performed in the same manner as in Example 1. The result is shown in FIG. Co-γ-MnO ₂ prepared in Example 3 did not show a significant change in activity even when the amount of hydrazine added was changed, but Co-γ-MnO ₂ prepared in Example 4 added hydrazine. Activity increased with increasing amount.

  Since the cobalt composite γ-type manganese dioxide of the present invention is excellent in activity for oxygen generation reaction, it can be suitably used as a catalyst for oxygen generation reaction in water electrolysis and the like. Moreover, it can be used as an electrode in a secondary battery or an air battery.

Claims (10)

  A cobalt composite γ-type manganese dioxide containing cobalt in the crystal structure.   A catalyst for oxygen generation reaction comprising the cobalt composite γ-type manganese dioxide according to claim 1.   A method for electrolyzing water, wherein the catalyst for oxygen generation reaction according to claim 2 is used as the catalyst for oxygen generation reaction.   An electrode comprising cobalt composite γ-type manganese dioxide according to claim 1 as a material constituting the electrode.   A secondary battery or an air battery comprising the electrode according to claim 4.   A method for producing a cobalt composite γ-type manganese dioxide, wherein a solution in which a cobalt salt and a reducing agent are dissolved is brought into contact with γ-type manganese dioxide and then dried.   A step of immersing and stirring γ-type manganese dioxide particles in a solution in which a cobalt salt and a reducing agent are dissolved, and a step of filtering the solution in which the γ-type manganese dioxide particles are immersed and drying the residue. A process for producing a cobalt composite γ-type manganese dioxide according to claim 6.   The method for producing a cobalt composite γ-type manganese dioxide according to claim 6 or 7, wherein the cobalt salt is cobalt chloride.   The method for producing a cobalt composite γ-type manganese dioxide according to any one of claims 6 to 8, wherein the reducing agent is hydrazine.   A cobalt composite γ-type manganese dioxide obtained by bringing a solution in which a cobalt salt and a reducing agent are dissolved into contact with γ-type manganese dioxide and then drying.

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