New insight into the mechanism of cathodic electrodeposition of zinc oxide thin films onto vitreous carbon

Abstract : In this study, the mechanism of zinc oxide (ZnO) electrodeposition from aqueous zinc nitrate solution at 70°C was investigated on vitreous carbon and bulk zinc electrodes using cyclic voltammetry experiments. Mechanisms are presented for the ZnO formation: the first widely accepted route corresponds to ZnO precipitation from Zn 2+ and OH-produced by NO3-reduction; the second route, which is discussed in this article, is due to Zn 2+ reduction into metallic Zn followed by its oxidation by nitrate ions. For this case, we demonstrate why Zn formation can not be observed while Zn 2+ reduction was detected. Structural and morphological of bulk deposits were investigated using X-ray diffraction and scanning electron microscopy. Well-oriented ZnO nanorods forming thin films were grown on vitreous carbon from Zn(NO3)2 solution at low cathodic potential corresponding to that of zinc metal deposition. X-ray diffraction (XRD) measurements showed that the nanorods are crystalline and preferably grown along the (002) direction.