THE ELECTROCHEMISTRY OF GOLD AT GLASSY-CARBON IN THE BASIC ALUMINUM CHLORIDE-1-METHYL-3-ETHYLIMIDAZOLIUM CHLORIDE MOLTEN-SALT

Gold(III) is complexed as [AuCl4]- in the basic aluminum chloride-1-methyl-3-ethylimidazolium chloride molten salt solvent. In contrast to the three-electron reduction process found at metal electrodes in molecular solvents, the voltammetric reduction of [AuCl4]- at glassy carbon in this solvent occurs in two steps with the intermediate formation of a gold(I) complex, most likely [AuCl2]-. Potentiometric and voltammetric measurements place the formal potentials of the Au(I)/Au and Au(III)/Au(I) couples at 0.374 +/- 0.002 and 0.310 +/- 0.002 V, respectively, in the 44.4-55.6 mole percent melt vs. the Al(III)/Al couple in the 66.7-33.3 m/o melt. Thus, gold(I) is observed as an intermediate during voltammetry experiments because the deposition of gold on glassy carbon requires a substantial nucleation overpotential. The oxidation of gold metal in basic melt produces stable solutions containing gold(I); the electrodeposition of gold from these solutions exhibits three-dimensional progressive nucleation with hemispherical diffusion-controlled growth of the nuclei. The diffusion coefficient for gold(I) in the 44.4-55.6 m/o melt measured using chronoamperometry is ca. 1.1 x 10(-6) cm2 s-1 at 40.0-degrees-C.