Effect of Ammonium Salts on the Conductivity and Current Efficiency of Dimethyl Sulfone-Aluminum Chloride Electrolytes

In this study, we investigated the effects of ammonium chloride (NH 4 Cl) and tetramethylammonium chloride (TMAC) on the conductivity and current efficiency of dimethyl sulfone (DMSO 2 )-aluminum chloride (AlCl 3 ) electrolyte. When NH 4 Cl and TMAC were added independently, the conductivity of the electrolyte increased, which was attributed to a decrease in the electrolyte viscosity. 27 Al nuclear magnetic resonance (NMR) spectroscopy showed that chloride addition reduced the ratio of solvated Al 3+ ions. This occurred because Al 3+ and Cl − dissociated from chloride and formed AlCl 4 − , which increased the amount of non-solvated DMSO 2 species, consequently decreasing the electrolyte viscosity. NH 4 Cl improved the plating appearance even when added in small amounts; however, when added in relatively high concentrations, the conductivity increased, while the current efficiency decreased significantly. Conversely, TMAC did not induce a significant decrease in the current efficiency up to an addition amount of 0.1 mol. The electrolyte with the co-addition of TMAC and a small amount of NH 4 Cl showed increased conductivity while minimizing the decrease in current efficiency. Also, good results in the appearance and purity of the plating film were obtained.