ALKALI-METAL REDUCTION POTENTIALS MEASURED IN CHLOROALUMINATE AMBIENT-TEMPERATURE MOLTEN-SALTS

Alkali metal electrochemical reductions at a mercury film electrode (MFE) were studied in AlCl3:MEIC (MEIC = 1-methyl-3-ethylimidazolium chloride) molten salts buffered to a neutral composition with MCl (M = Li, Na, K, Rb, and Cs). The MFE was formed by mercury deposition on a 127-mu-m iridium disk electrode. At the Ir-MFE, the reduction potentials for the Li, Na, K, Rb, and Cs amalgams were observed at -1.16, -1.26, -1.62, -1.67, and -1.75 V (vs. Al/Al(III)), respectively. By comparison of the amalgam reduction potentials in the melts to aqueous data, the formal reduction potentials for the elemental alkali metals in the buffered neutral melts are calculated to be -2.14, -2.15, -2.71, -2.77, and -2.87 V (vs. Al/Al(III)), for Li, Na, K, Rb, and Cs, respectively. The solvation energies for the alkali metals in the chloroaluminate molten salts are calculated to be approximately 4 to 15% lower than aqueous solvation energies.