Effect of the Anodic Titania Layer Thickness on Electrodeposition of Zinc on Ti/TiO2 from Deep Eutectic Solvent

Zinc electrodeposition from a deep eutectic mixture of ZnCl2 and choline chloride/ethylene glycol on titanium covered by an anodic titania film of different thicknesses was studied. It was shown that thin titanium dioxide layers work as high resistive media and the rate of zinc deposition decreases with film thickness. Thicker titania layers (23 nm and higher) have opposite properties and the zinc reduction rate starts gradually increasing with thickness. This happens because at the higher voltage necessary to grow thicker anodic films they become more crystalline and consequently more conductive. There is also evidence that in deep eutectic solvent no dense organic layer forms on the titanium/titania electrodes. The application of an AC signal superimposed on a DC potential only marginally increases the amount of zinc deposited and FTIR measurements did not reveal the formation of any chemical bonds between the film and deep eutectic solvent. Zn deposition onto titanium/titania at -1.6 V is characterized by instantaneous three-dimensional nucleation mechanism, which is independent of the titania thickness. (C) 2017 The Electrochemical Society. All rights reserved.