Characterization of Imidazolium Chloride Ionic Liquids Plus Trivalent Chromium Chloride for Chromium Electroplating

A series of mixtures consisting of the ionic liquids (ILs) 1-ethyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium chloride, and 1-hexyl-3-methylimidazolium chloride ([emim][Cl], [bmim][Cl], and [hmim][Cl], respectively) and trivalent chromium chloride have been prepared. Physicochemical and electrochemical properties of these mixtures have been studied and the potential applications of these mixtures for chromium electroplating, as an alternative to the conventional hard chromium electroplating processes using hexavalent chromium baths, have been examined. To optimize the transport properties of the mixtures, different amounts of ultrapure water were added to the Cr(III) salt–IL mixtures, although the ultimate goal is to reduce or eliminate water. As shown previously for choline chloride/Cr(III) salt mixtures, we found that the physicochemical and electrochemical properties of the mixtures are affected by the relative water content. Our preliminary electroplating results show that these types of Cr(III) salt–IL mixtures could be promising alternatives to Cr(VI) containing baths for chromium electroplating applications with the advantage of avoiding the use of highly toxic hexavalent chromium.