Fabrication of nano-structured zinc oxides on zinc foils in alkaline zinc containing solutions by a potentiostatic process

This work attempts to fabricate nano-structured zinc oxides on zinc foils in alkaline solutions containing zinc ions by electrochemical oxidation. After grinding and polishing, the zinc foil was potentiodynamically polarized in alkaline solutions (i.e. 2 M NaOH) with and without 0.25 M Zn(NO ₃ ) ₂ and 0.25 M NaNO ₃ . The polarization process was carried out using a potentiostat with sweeping potentials starting from 0.250 V below the open circuit potentials towards 2.000 V (vs. SHE) with a scan rate of 1 mV/s. Based on the polarization diagram, we chose four characteristic potentials (i.e., -0.5 V, -0.7 V, -0.9 V, and -1.1 V vs. SHE) at which potentiostatic polarizations were conducted on polished zinc plates (as the working electrodes) with respect to a counter electrode of 304 stainless steel and an Ag/AgCl _sat reference electrode. The potentiostatic experiments were carried out in 2 M NaOH solutions with 0.25 M Zn(NO ₃ ) ₂ for 1 hour and corresponding currents were measured. According to examinations via FE-SEM, we found that nano-wires of zinc oxide were produced at higher potentials (e.g., -0.5 V and -0.7 V) but nanoplates of zinc oxide formed at lower potentials (e.g., -0.9 V and -1.1 V). EDX analyses over the nano wires and the nano plates indicated an atomic ratio of Zn to O at almost one. In addition, the presence of Zn(2p _3/2 ) at 1021.9 eV was confirmed by XPS, which ensured the oxide form of the nanostructures.