Voltammetric Study and Electrodeposition of Zinc in Hydrophobic Room-Temperature Ionic Liquid 1-Butyl-1-methylpyrrolidinium Bis((trifluoromethyl)sulfonyl)imide ([BMP][TFSI]): A Comparison between Chloride and TFSI Salts of Zinc

Abstract

The voltammetric behavior, nucleation mechanism, and electrodeposition of zinc were carefully studied in hydrophobic room-temperature ionic liquid 1-butyl-1-methylpyrrolidinium bis((trifluoromethyl)sulfonyl)imide (RTIL [BMP][TFSI]). The Zn(II) species were introduced via the anodic dissolution of Zn, or the addition of Zn(TFSI)2 and ZnCl2, respectively. Unexpectedly, ZnCl2 shows a high solubility in [BMP][TFSI] where most metal chlorides are almost insoluble. For electrodeposition, ZnCl2 hence can be used as a cheaper and time-saving alternative of the Zn(II) source. Two Zn salts show obviously different voltammetric behavior, which may result from the different Zn(II) species formed. Two redox couples of Zn(II) are observed in ZnCl2 solutions but there is only one redox couple in Zn(TFSI)2 solutions. Many phenomena imply that two Zn(II) species, one is partially Cl-coordinated and the other one is TFSI-coordinated, are produced from ZnCl2. The surface morphology of Zn deposits prepared from the two Zn salts at 80°C is not distinguishable but apparently changed with the electrodepositing potential. Similarly, the nucleation mechanism is independent of the Zn salts, and a 3-dimensional (3D) progressive nucleation with diffusion controlled growth is observed. Oppositely, the deposition/stripping efficiency of Zn is significantly influenced by the source of Zn(II); a much higher efficiency is observed in the Zn(TFSI)2 solutions.