Simple transition metal oxides such as NiO, Co3O4, Fe3O4 and Cu2O were found to catalytically decompose water into H2 and O2 by mechanical energy. The reaction is regarded as `mechano-catalytic' overall water splitting' and is a quite novel catalytic reaction. In this paper, some general aspects on the mechano-catalytic overall water splitting are reviewed on simple oxides. In addition, recent results on the mechano-catalytic activity of a groups of mixed oxides, wolramite-type oxides with a formula of ABO4 (A = Fe, Co, Ni and Cu, etc., B = W, Mo), are shown. AWO4 (A = Fe, Co, Ni and Cu) decomposed water into H2 and O2 under the supply of mechanical energy, indicating that mechano-catalytic overall water splitting proceeded on wolframite-type compounds containing 3d-transition metals. AMoO4 (A = Fe, Co, Ni) also decomposed water into H2 and O2 under supply of mechanical energy. The reaction properties on wolframite-type oxides are discussed.
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