Abstract: To provide a manganese-iridium composite oxide, a manganese-iridium composite oxide and a manganese-iridium composite oxide electrode material, having high catalytic activity produced at low cost, to be used as an anode catalyst for oxygen evolution in water electrolysis, and their production methods. A manganese-iridium composite oxide, which has an iridium metal content ratio (iridium/(manganese+iridium)) of 0.1 atomic % or more and 30 atomic % or less, and has interplanar spacings of at least 0.243±0.002 nm, 0.214±0.002 nm, 0.165±0.002 nm, 0.140±0.002 nm, and a manganese-iridium composite oxide electrode material comprising an electrically conductive substrate constituted by fibers at least part of which are covered with the above manganese-iridium composite oxide.

Abstract: To provide a manganese-iridium composite oxide, a manganese-iridium composite oxide and a manganese-iridium composite oxide electrode material, having high catalytic activity produced at low cost, to be used as an anode catalyst for oxygen evolution in water electrolysis, and their production methods. A manganese-iridium composite oxide, which has an iridium metal content ratio (iridium/(manganese+indium)) of 0.1 atomic % or more and 30 atomic % or less, and has interplanar spacings of at least 0.243±0.002 nm, 0.214±0.002 nm, 0.165±0.002 nm, 0.140±0.002 nm, and a manganese-iridium composite oxide electrode material comprising an electrically conductive substrate constituted by fibers at least part of which are covered with the above manganese-iridium composite oxide.

Abstract: The present invention provides a water electrolysis method comprising: supplying at least water into an electrolysis cell which includes a solid polymer electrolyte membrane, and an anode and a cathode disposed sandwiching the solid polymer electrolyte membrane therebetween; and providing a potential P between the anode and the cathode to generate oxygen from the anode, wherein an oxidation catalyst containing at least one of first transition metals is present on at least a part of a surface of the anode, and the potential P satisfies P1<P<P2, wherein P1 indicates a lowest potential at which oxygen is generated from the anode, and P2 indicates a lowest potential P2 at which a quantitative index of a dissolved chemical species derived from the oxidation catalyst begins to show potential dependence.

Abstract: The present invention provides a water electrolysis method comprising: supplying at least water into an electrolysis cell which includes a solid polymer electrolyte membrane, and an anode and a cathode disposed sandwiching the solid polymer electrolyte membrane therebetween; and providing a potential P between the anode and the cathode to generate oxygen from the anode, wherein an oxidation catalyst containing at least one of first transition metals is present on at least a part of a surface of the anode, and the potential P satisfies P1<P<P2, wherein P1 indicates a lowest potential at which oxygen is generated from the anode, and P2 indicates a lowest potential P2 at which a quantitative index of a dissolved chemical species derived from the oxidation catalyst begins to show potential dependence.

Abstract: A manganese oxide, a manganese oxide/carbon mixture and a manganese oxide composite electrode material, having high catalytic activity produced at low cost, to be used as an anode catalyst for oxygen evolution in water electrolysis, and their production methods, are provided. A manganese oxide for an oxygen evolution electrode catalyst in water electrolysis is provided, which is a manganese oxide having a metallic valence of higher than 3.0 and at most 4.0, having an average primary particle size of at most 80 nm and an average secondary particle size of at most 25 ?m, a manganese oxide/carbon mixture for an oxygen evolution electrode catalyst in water electrolysis, having a proportion of manganese oxide to the total of the manganese oxide and electrically conductive carbon of from 0.5 to 40 wt %, and a manganese oxide composite electrode material which includes an electrically conductive substrate constituted by fibers.