Electrochemistry of vanadium oxides and oxyhalides in chloroaluminate room temperature ionic liquids

The electrochemistry of several vanadium oxides and oxyhalides has been examined in room temperature ionic liquids made by mixing 1-ethyl-3-methylimidazolium chloride (EMIC) and aluminum chloride. By varying the mole ratio of the two components, Lewis basic, neutral, and acidic ionic liquids were formed, while the addition of NaCl to an acidic ionic liquid resulted in a Lewis buffered, neutral solvent. Because of the ionic nature of these liquids, most oxides have very low solubility: V2O3,V2O4, and VOSO4 are insoluble, while V2O5 and Na3VO4 are slightly soluble with solubility limits of less than 5 mM. The solubilities of the salts NaVO3 and NH4VO3 and the oxyhalides VOCl3 and VOF3 are significantly higher. In acidic ionic liquids, V2O5, NaVO3, Na3VO4, and NH4VO3 all exhibit three irreversible reduction waves between 1.7 and 0.5 V vs. a reference electrode consisting of an aluminum wire in a 0.6 mole fraction AlCl3 ionic liquid. VOCl3 and VOF3 gave similar reduction peaks, suggesting that the oxides may have reacted with the ionic liquid to form oxychlorides. A new ionic liquid was formed by using VOCl3 as the Lewis acid instead of AlCl3 EMIC + VOCl3 --> [EMI](+) + [VOCl4](-) In acetonitrile [VOCl4](-) underwent a one-electron reversible reduction to [VOCl4](2-) [VOCl4](-) + e(-) <--> [VOCl4](2-) (C) 2002 The Electrochemical Society.