THE ELECTROCHEMISTRY OF TIN IN THE ALUMINUM CHLORIDE-1-METHYL-3-ETHYLIMIDAZOLIUM CHLORIDE MOLTEN-SALT

The electrochemistry of Sn(II) and Sn(IV) was studied with voltammetry and chronoamperometry at polycrystalline Pt and Au and at glassy carbon (GC) electrodes in the acidic and basic aluminum chloride-1-methyl-3-ethylimidazolium chloride (AlCl3-MeEtimCl) molten salt at 40-degrees-C. The Sn(II) reduction process is uncomplicated at Pt. The underpotential deposition of a Sn monolayer is observed at Au; an additional UPD process is attributed to surface alloy formation. The deposition of Sn on GC is complicated by nucleation. Experimental current-time transients recorded at GC electrodes are in good agreement with theoretical models based on three-dimensional nucleation with diffusion-controlled growth of the nuclei. The formal potentials of the Sn(II)/Sn couple in the 66.7-33.3 and 44.4-55.6 mole percent melts are 0.55 +/- 0.01 and -0.85 +/- 0.03 V, respectively vs. Al(III)/Al in the 66.7-33.3 mole percent melt. Diffusion coefficients of Sn(II) in these melts are (5.3 +/- 0.7) x 10(-7)and (5.1 +/- 0.6) x 10(-7) cm2 s-1, respectively. The voltammetric oxidation of Sn(II) to Sn(IV) is hindered by the weak adsorption of Sn(II). The Sn(IV)/Sn(II) electrode reaction displays very sluggish heterogeneous kinetics. Sn(IV) is complexed as [SnCl6]2- in basic melts.