Low Temperature Electrochemical Deposition of Aluminum in Organic Bases/Thiourea-Based Deep Eutectic Solvents

In this study, a series of novel quasi-deep eutectic solvents (QDESs) based on organic base and thiourea (TU) and its derivatives were formed. Among them, DBU/TU or methylthiourea (MTU) could be used for the formation of the stable γ-Al2O3 colloid at quite a high concentration (0.6 mol %), which was verified by small-angle X-ray scattering (SAXS) experiments. The solution is highly fluidic with a viscosity of 46.2 mPa·s at 50 °C. The attenuated total reflection infrared spectra (ATR-IR), 27Al nuclear magnetic resonance (NMR), and density functional theory (DFT) calculation proved that γ-Al2O3 was coordinated with the sulfur atom of methylthiourea. Electrodepositing of aluminum from the system at a low temperature (50 °C) and atmospheric environment was achieved. The cyclic voltammogram indicated a good aluminum deposition peak at −0.26 V at 50 °C. SEM, EDS, and XRD pattern showed that homogeneous, pure, and adherent aluminum layers were obtained. Moreover, these DESs are versatile and can be used for dissolving other metals, metal sulfides, and metal oxides, including CoO, NiO, Ni2O3, MoO3, CuS, Fe, W, Cu, and V2VI3 chalcogenides. Therefore, this work extended the scope of green solvent and made an improvement in both low temperature electrolytic alumina and solution processing of other metal-based materials.