Ni nanotube arrays are fabricated using a facile, one-pot, and template-free method by electroplating Cu-Ni core-shell microcolumns followed by electrochemical dealloying of Cu. Well-separated Cu-Ni core-shell microcolumns are first formed as a result of controlled electrodeposition rates of Ni and Cu and the existence of miscibility gap for Ni-Cu alloys. Cu is more rapidly deposited onto the substrate forming cores that serve as the template to be coated with less rapidly deposited Ni species, producing Cu-Ni core-shell microcolumns. Ni nanotube arrays are then generated by selectively etching away the Cu cores. The Ni nanotube arrays thus obtained possess attractive anti-reflection, superhydrophobicity, and magnetic properties.