Method for manufacturing nanostructured manganese oxide having dendritic structure, and oxygen reduction electrode comprising nanostructured transition metal oxide having dendritic structure

1. A method for manufacturing a nanostructured manganese oxide having a dendritic structure formed from an agglomeration of primary particles, wherein the method comprises the steps of:

removing components from a target plate that comprises one or more kinds of manganese oxides by irradiating the target plate with laser light in an atmosphere comprising a mixed gas of inert gas and oxygen gas, the content of the oxygen gas in the mixed gas being no less than 0.05% but no more than 0.5% as measured by mass flow rate; and

depositing the removed components on a substrate that is opposed to the target plate substantially in parallel to obtain the nanostructured manganese oxide.

2. The method of claim 1 , wherein the oxygen reduction potential of the nanostructured manganese oxide is −0.2 V in a cyclic voltammogram employing a cyclic voltammetry, the cyclic voltammetry using a three electrode cell in which the nanostructured manganese oxide is used as the working electrode, platinum is used as the counter electrode, silver/silver chloride is used as the reference electrode, and an aqueous 0.1 mol/l potassium hydroxide solution at pH 13 is used as the electrolyte.

3. The method of claim 1 , wherein the inert gas is helium.

4. The method of claim 1 , wherein the atmosphere is activated by being energized.

5. The method of claim 1 , wherein the atmosphere has a pressure of at least 13.33 Pa but no more than 1333 Pa.

6. The method of claim 1 , wherein the laser light is a pulsed laser light which has a pulse duration of at least 5 ns but no more than 20 ns.

7. The method of claim 1 , wherein the laser light has an energy density of at least 0.5 J/cm 2 but no more than 2 J/cm 2 .

8. The method of claim 1 , wherein the target plate is a manganese oxide sintered body.

9. The method of claim 1 , which further comprises a step of heating the obtained nanostructured manganese oxide.

10. The method of claim 1 , wherein the pressure of the atmosphere is varied.

11. The method of claim 1 , which further comprises a step of positioning the target plate and the substrate in a reaction system in such a manner that they are opposed to each other in parallel prior to all the other steps.

12. The method of claim 1 , which further comprises a step of controlling at least one of 1) the pressure of the atmosphere, and 2) the distance between the target plate and the substrate, in order to control the size of the high-temperature and high-pressure region that is formed in the vicinity of the target plate by irradiating the target plate with laser light.

13. An oxygen reduction electrode comprising:

a nanostructured manganese oxide having a dendritic structure formed from an agglomeration of primary particles, wherein

the primary particles having a mean diameter of at least 2 nm, but no more than 20 nm and

the oxygen reduction potential of the nanostructured manganese oxide is −0.2 V in a cyclic voltammogram employing a cyclic voltammetry, the cyclic voltammetry using a three electrode cell in which the nanostructured manganese oxide is used as the working electrode, platinum is used as the counter electrode, silver/silver chloride is used as the reference electrode, and an aqueous 0.1 mol/l potassium hydroxide solution at pH 13 is used as the electrolyte.

14. The oxygen reduction electrode of claim 13 , wherein the dendritic structure has a mean height of at least 1 μm but no more than 20 μm.

15. The oxygen reduction electrode of claim 13 , wherein the nanostructured manganese oxide comprises at least one manganese oxide selected from the group consisting of manganese monoxide, trimanganese tetroxide, dimanganese trioxide and manganese dioxide.

16. The oxygen reduction electrode of claim 13 , wherein the nanostructured manganese oxide is formed on an electrically conductive substrate.

17. The oxygen reduction electrode of claim 15 , wherein the nanostructured manganese oxide is formed on an electrically conductive substrate.