Zinc Nanoparticles Electrodeposited on TiO₂Nanotube Arrays Using Deep Eutectic Solvents for Implantable Electrochemical Sensors

This work reports on the electrodeposition of zinc on nanoporous metal oxide titania nanotube arrays (TiO 2 NTAs) using a zinc-containing deep eutectic solvent (Zn 2+ –DES). The effects of substrate morphology and crystallinity, deposition temperature, zinc concentration, and deposition time on the morphology and electrochemical properties of the Zn/TiO 2 NTAs were investigated. Two-dimensional zinc nanohexagons (NHexs) with a mean diameter of ∼300 nm and a thickness of 10–20 nm were decorated onto the TiO 2 NTAs (with a pore diameter of ∼80 nm and a tube length of ∼5 μm) via electrodeposition at −1.6 V using Zn 2+ –DES. Cyclic voltammetry tests on the Zn 2+ –DES electrolyte revealed an electrochemical window of ∼3.5 V, and the diffusion coefficient of Zn 2+ was found to be 4.29 × 10 –10 cm 2 s –1 at room temperature and 7.10 × 10 –10 cm 2 s –1 at 40 °C. Zinc nucleation on TiO 2 NTA substrates followed an instantaneous model. Using a higher electrodeposition temperature increased the nucleation and growth rate of zinc NHexs, while annealing TiO 2 NTAs was found to improve their uniformity and morphology. During the initial stage of deposition, hexagonal close-packed zinc NHexs were found to preferentially grow on tetragonal anatase TiO 2 NTAs. The electrodeposition of zinc resulted in lowering the impedance and improving the overall electrochemical properties of TiO 2 NTAs. The Zn/TiO 2 NTAs developed in this study offer a promising electrocatalyst material system for implantable electrochemical sensors.