[en] By deintercalation of Na⁺ followed by inserting bilayers of water molecules into the host lattice, the layered cobalt oxide of γ-Na_0.7CoO₂ undergoes a topotactic transformation to a layered cobalt oxyhydrate of Na_0.35(H₂O)_1.3CoO_2-δ with the c-axis expanded from c ∼ 10.9 A to c ∼ 19.6 A. In this paper, we demonstrate that the superconducting phase of c ∼ 19.6 A can be directly obtained by simply immersing γ-Na_0.7CoO₂ powders in electrolyzed/oxidized (EO) water, which is readily available from a commercial electrolyzed water generator. We found that high oxidation-reduction potential of EO water drives the oxidation of the cobalt ions accompanying by the formation of the superconductive c ∼ 19.6 A phase. Our results demonstrate how EO water can be used to oxidize the cobalt ions and hence form superconducting cobalt oxyhydrates in a clean and simple way and may provide an economic and environment-friendly route to oxidize the transition metal of complex metal oxides