Speciation of cobalt-chloride-based ionic liquids and electrodeposition of Co wires

• Template-free electrodeposition of cobalt nanowires arrays can be achieved from Lewis acidic CoCl2-EMIC ionic liquids.
• SEM and TEM images reveal the diameter of the nanowire is around 200 nm, and the XPS data shows that cobalt oxide is formed at the surface of the nanowire.
• MALDI-TOF-MS, XAS, and UV-vis spectroscopy results show that the coordination number and the mean Co-Cl bond length are depending on the molar ratio of CoCl2 and EMIC.

The speciation and coordination of cobalt-chloride-based ionic liquids with various mole percentages of CoCl2 were investigated using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), X-ray absorption spectroscopy (XAS), ultraviolet-visible absorption spectroscopy, and cyclic voltammetry. The coordination number and the mean Co-Cl bond length decreases with increasing CoCl2 concentration, indicating that various Co(II) chloride compounds such as CoCl42-, Co2Cl5-, and Co3Cl7− are formed depending on the molar ratio of CoCl2 and EMIC in the melt. While the [CoCl4]2− complex formed in the Lewis basic melts and is electrochemically inactive within the electrochemical window of the melt, the other coordination-unsaturated cobalt chloride compounds formed in Lewis acidic melts can be electrochemically reduced to cobalt metal. The template-free electrodeposition of Co nanowires can be achieved from 40-60 mol% and 50-50 mol% CoCl2-EMIC (1-ethyl-3-methylimidazolium chloride) ionic liquids without any additives. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) were used to characterize the surface of the deposits.