Electrochemical investigations in basic alkali chloroaluminate melts

Alkali chloroaluminate melts, such as the AlCl₃/NaCl melt, have drawn considerable interest as aprotic media for chemical, electrochemical and various spectroscopic studies. These melts are characterized by relatively low melting points, large decomposition potentials, and a wide optical transparency range. The acid-base properties of these melts can be varied over a wide range by changing the melt composition.

The utility of ultramicroelectrodes for electrochemical studies in AlCl₃/NaCl_sat melts has been demonstrated by using iron(III) chloride as a probe system. Cyclic voltammetric and normal pulse voltammetric results obtained at a tungsten disk ultramicroelectrode were compared to the results obtained at a conventional tungsten disk electrode. Several improvements resulting from the use of ultramicroelectrodes with respect to conventional electrodes were observed in this research.

The electrochemical and spectroscopic studies. of [Bu₄]₂[Re₂Cl₈] and K₂[ReCl₆] in the AlCl₃3/NaCl_sat melt are also reported in this thesis. UV-visible absorption spectroscopic studies reveal that [Re₂Cl₈]^2- and [ReCl₆]^{2- are stable in the AlCl₃/NaCl_sat melt. Cyclic voltammetry (CV), normal pulse. voltammetry (NPV) and controlled potential electrolysis were used to study the reduction of these species. Cyclic voltammograms and normal pulse voltammograms exhibit two iv reduction waves. The first reduction peak of [Re₂Cl₈]2- involves an EC mechanism in which [Re₂Cl₈]2- is first reduced to [Re₂Cl₈]3-. The species [Re₂Cl₈]3- is not stable in this melt and is converted to some unknown species. Electrochemical and spectroscopic results suggest that the initial reduction of [ReCl₆]2- involves an ECEC mechanism in which [ReCl₆]2- is first reduced to [ReCl₆]3-. This species is unstable in the melt and dimerizes to give [Re₂Cl₈]2-, which has a reduction potential more positive than that of [ReCl₆]2-, and therefore is immediately reduced to [Re₂Cl₈]3- which is converted to some unknown species. Finally, the addition of Re₃Cl₉, to the AlCl₃/NaCl_sat melt produced [ReCl₆]2- and an unknown solid.}