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

Abstract

In this study, we investigated the effects of ammonium chloride (NH4Cl) and tetramethylammonium chloride (TMAC) on the conductivity and current efficiency of dimethyl sulfone (DMSO2)-aluminum chloride (AlCl3) electrolyte. When NH4Cl and TMAC were added independently, the conductivity of the electrolyte increased, which was attributed to a decrease in the electrolyte viscosity. 27Al nuclear magnetic resonance (NMR) spectroscopy showed that chloride addition reduced the ratio of solvated Al3+ ions. This occurred because Al3+ and Cl− dissociated from chloride and formed AlCl4 −, which increased the amount of non-solvated DMSO2 species, consequently decreasing the electrolyte viscosity. NH4Cl 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 NH4Cl showed increased conductivity while minimizing the decrease in current efficiency. Also, good results in the appearance and purity of the plating film were obtained.