The role of additives in the electroreduction of sodium ions in chloroaluminate-based ionic liquids

Ionic liquids are an ionically conductive medium that can provide a wide potential window for the study of electrochemical processes. We have observed that the degree of ionization of the ions depends on the charge density of the ions with significant ion pairing possible. Previously, it was shown that sodium ions can be reduced only to sodium metal if an acidic additive (e.g., SOCl2) is added to the liquid. It is shown here that the additive increases the degree of dissociation of the Na+ from its counterion in the liquid, making it available for electrodeposition. The observed increase in ionic conductivity provided by the SOCl2 supports this proposed mechanism. It is believed that the additive coordinates with chloride in the liquid, to provide greater freedom for the Na+ ion. In addition, conditions were found for the reduction of sodium ions to sodium metal without the use of an additive. (C) 2004 The Electrochemical Society.