Influences of metal-precoated layers on pulsed current electrodeposition of ZnO nanorods on indium tin oxide substrates

The influences of the Au- and Pt-precoated layers on ZnO nanorod growth have been investigated using the pulsed current electrodeposition method. Enhancement of the densities of the ZnO nanorod arrays is achieved using both metal-coated indium tin oxide (ITO) substrates whereas more significant improvement is obtained using the Au-precoated substrates. Tafel-plot analyses for the reaction of O H- formation by NO₃- and H₂O, which is a crucial step for the electrodeposition of ZnO using Zn (NO ₃)₂ electrolyte reveal that O H- formation through this reaction occurs in the limiting-current region at the Au/ITO substrate in the ZnO nucleation stage while the side reaction of H₂ formation also takes place at the Pt/ITO and the bare ITO substrates under the same pulse current density in this study. We suggest that the low-density ZnO nanorods formed on the Pt-precoated and the bare ITO substrates are ascribed to the formation of H₂ which would influence [O H-] on the surface. Because of an appropriate potential build up at the Au/ITO substrate, a high [O H-] exists on the surface of the Au/ITO substrate without being disturbed by H ₂ significantly, resulting in high-density ZnO nanorods deposited on the Au/ITO substrates.