THE LEWIS ACIDITY OF ROOM-TEMPERATURE CHLOROALUMINATE MOLTEN-SALTS BUFFERED WITH SODIUM-CHLORIDE

The electrochemistry of a NaCl-buffered, MEICl/AICl3 (MEICl = 1-methyl-3-ethylimidazolium chloride) melt was studied using Pt and W electrodes. When excess NaCl is added to an N = 0.55 melt (N = the mole fraction AlCl3) a neutral melt results, saturated with NaCl. The cyclic voltammetry shows several small overlapping reduction peaks which lead to a small, but distinct oxidation peak about -0.1 V (vs. an Al/Al3+ N = 0. 6 melt reference). Comparison to the voltammogram of an N = 0.5002 melt (no NaCl) suggests that the oxidation process is aluminum stripping. A series of plating and stripping experiments and scanning electron microscopic (SEM) examination of the electrode surfaces verify this. The presence of the Al stripping peak in the voltammogram of the buffered melt means that this melt is still slightly Lewis acidic even when saturated with NaCl. The concentration of Al2Cl7- in the buffered melt is estimated to be 2.8 x 10(-3) M. This is considerably higher than the calculated equilibrium concentration for Al2Cl7- of 4.6 x 10(-8) M corresponding to a truly Lewis natural melt.