On the Electrodeposition of Titanium from TiCl4 in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide: In Situ AFM and Spectroscopic Investigations

Abstract

Obtaining titanium (Ti) coatings on industrially relevant materials at room temperature would be beneficial due to its excellent corrosion resistance and strength. Ionic liquids (ILs) have been discussed as electrolytes for this purpose, but, efforts to electrodeposit titanium from its halide sources in ILs failed due to titanium subhalide formation. Herein, we have investigated the electrode/electrolyte interface (EEI) of TiCl4 in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide, [Py1,4]TFSA, with a focus on the changes in the nanostructure at varying concentrations of the Ti precursor using Atomic Force Microscopy (AFM). Furthermore, the solution species of varying TiCl4 concentrations were investigated by Raman Spectroscopy. The AFM results reveal that the concentration of TiCl4 influences strongly the interfacial nanostructure of the Au(111)/electrolyte interface. A typical ‘IL’ multilayered structure can be seen upon adding 0.1 M TiCl4 to the IL, which disrupts completely upon further increasing the concentration to ≥ 0.25 M. Furthermore, the AFM force-distance profiles showed that quite soft films have been formed on the electrode surface under electrolysis conditions, which could influence the reduction processes to obtain elemental Ti. Our results reveal that the concentration of TiCl4 can influence strongly the EEI nanostructure and can provide some new fundamental insights into the double layer structure of TiCl4 in [Py1,4]TFSA.