Voltammetric behavior of Zn(II) introduced into the room temperature ionic liquid 1-butyl-1-methylpyrrolidinium bis((trifluoromethyl)sulfonyl)imide (RTIL BMP-TFSI) via the addition of ZnCl₂ or Zn(TFSI)₂ salt was studied. It is surprised that ZnCl₂ is highly soluble in this IL because many transition metal chlorides are insoluble in the TFSI-based ILs, leading to the retardation of applying the RTIL BMP-TFSI to electrodeposition. Two redox couples both associated to the redox reaction Zn(II) + 2e⁻ ↔ Zn were observed in the ZnCl₂ solution, which resulted from the nonchloride-coordinated and chloride-coordinated Zn(II) species, respectively. However, a single redox couple corresponding to Zn(II) + 2e⁻ ↔ Zn was observed in the Zn(TFSI)₂ solution (Figure 1). According to the experiments of voltammetric titration, it was supposed that TFSI anions exhibit much stronger coordinating ability towards Zn²⁺ ions than to other common transition metal ions, resulting in the high solubility of ZnCl₂ in BMP-TFSI. A sufficient amount of chloride anion must be introduced in order to observe the chloride-coordinated Zn(II) species in the Zn(TFSI)₂ solution. Afterwards, TFSI anions coordinated to Zn²⁺ ions were gradually replaced by chloride ions continuously introduced into the Zn(TFSI)₂ solution. Finally, no zinc redox couple could be observed once Zn²⁺ions were completely coordinated with chloride ions.

    Electrodeposition of Zn was achieved by potentiostatic electrolysis using copper substrates as the electrodes from the IL containing ZnCl₂ and Zn(TFSI)₂, respectively. Crystalline Zn could be obtained from the two different solutions. The crystallinity and surface morphology of the Zn electrodeposits depended on the applied potentials, and nanostructured Zn could be obtained at some particular electrodepositing potentials. An interesting current-vibration behavior was observed during the potentiostatic electrodeposition of Zn from ZnCl₂ solution, and this vibration behavior obviously depended on the applied potentials. It was supposed that the current-vibration behavior was due to a chloride-releasing & chloride-combination mechanism accompanied with the diffusion-drove supplementary of electroactive Zn(II) species because the vibration phenomenon was only observed while the applied potentials were set at where the chloride-coordinated Zn(II) species was reduced in the ZnCl₂ solution.