Electrochemical reduction mechanisms and stabilities of some cation types used in ionic liquids and other organic salts

This work presents the specific reduction reactions that may occur at the negative electrode whenever organic cations, particularly those used in ionic liquids, are used in an electrochemical application. The 1,3-dialkylimidazolium, 1,2,3-trialkylimidazolium, quaternary ammonium, morpholinium, sulfonium, phosphonium and pyridinium families of cations are covered in depth. Drawn from a review of the key literature, a range of mechanisms are presented, which will help the user of organic cations to predict reduction behaviour at the negative electrode, rationalise experimental observations and to design or choose salts that exhibit a desired electrochemical characteristic. The reduction potential of each cation type is also critically assessed. Although written primarily in the context of ionic liquids, the information presented in this work is relevant to any organic electrolyte system containing such cations.