Speciation, Conductivities, Diffusivities, and Electrochemical Reduction as a Function of Water Content in Mixtures of Hydrated Chromium Chloride/Choline Chloride

We report experiments and simulations to understand the factors that control chromium (Cr3+) electrodeposition from ionic liquid solutions. Speciation, conductivities and diffusivities in mixtures of trivalent chromium chloride, water and choline chloride (CrCl3/xH(2)O/yChCl) were computed from molecular dynamics simulations and compared to measured ultraviolet-visible spectra, conductivities from electrical impedance spectroscopy, and cyclic voltammograms. Computed changes in Cr3+ first solvation shell and conductivity with solution composition qualitatively agree with experimental observations. The Cr3+ first solvation shell contains predominantly H2O and Cl and the proportion of the two ligands changes with the relative bulk concentrations of each. Conductivities and diffusivities are observed to be functions of these composition variables. Variations in observed reduction current are primarily determined by dynamical properties and are less influenced by speciation.