Electrochemistry of thallium in the basic aluminum chloride-1 -methyl-3-ethylimidazolium chloride room temperature molten salt

The electrochemistry of thallium was studied in the basic aluminum chloride-l-methyl-3-ethylimidazolium chloride molten salt at 3O°C. In this basic melt system, thallium (III) chloride is complexed as [TlCl₆]^3- and can be electrochemically reduced to a Tl(I) species. The T1(III)/(I) electrode reaction exhibits slow charge-transfer kinetics with a standard heterogeneous rate constant of 1.82 × 10^-7 cm s^-1 and a cathodic transfer coefficient of ca. 0.2 in the 44.4/55.6 mole percent (mol %) melt. The formal potential of this redox couple is dependent upon the chloride concentration of the basic melt, suggesting the loss of two chloride ions from [TlCl₆]^3- coordination sphere during reduction to produce [TlCl₄]^3-) which could be further reduced to thallium metal. The formal potentials of the Tl(I)/Tl couple in the 44.4/55.6 and 40.0/60.0 mol % melts are -0.965 and -0.900 V, respectively, vs. Al(III)/Al in the 66.7/33.3 mol % melt. The electrodeposition of thallium on both tungsten and nickel electrodes proceeds via instantaneous three-dimensional nucleation.