Abstract : In article number 1901260, Hyoungjeen Jeen, Hiromichi Ohta, and co‐workers visualize the fast topotactic electrochemical oxidation reaction of SrCoO x oxygen sponge. The columnar oxidation from insulating SrCoO2.5 to metallic SrCoO3−δ occurs along the surface normal direction and then spread in the perpendicular to the normal direction.