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.