Mechano-catalytic overall water splitting on Cu2O, NiO, and Co3O4 was investigated in order to reveal the reaction mechanism. The experimental results indicated that metallic elements of these oxides were generated during the reaction. Also, elemental metals Cu, Ni, and Co were oxidized into Cu2O, NiO, and Co3O4, respectively, when water was reduced into H2 by the metal powders under the same reaction condition. The metallic particles covered with the metal oxides evolved both O2 and H2. These results suggest that a redox reaction between the metal and metal oxide may be responsible for H2 and O2 formation of the mechano-catalytic overall water splitting.

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