Electrochemical Stability of Imidazolium Based Ionic Liquids Containing Cyano Groups in the Anion: A Cyclic Voltammetry, XPS and DFT Study

The electrochemical stability of ionic liquids based on the 1-ethyl-3-methyl imidazolium [EMIM]+ cation and three different anions, dicyanoamide ([N(CN)2]−), tricyanomethanide ([C(CN)3]−) and tetracyanoborate ([B(CN)4]−), has been investigated. Cyclic voltammetry, X-ray photoelectron spectroscopy (XPS) of the valence band, as well as density functional theory (DFT) calculations were performed. A clear dependence of the anodic stability on the anion can be observed by cyclic voltammetry which is confirmed by XPS valence band spectra. The experimental data are in good agreement with DFT calculations. The valence band spectra and the DFT calculations of the ionic liquids show energetic differences in the position of the highest occupied molecular orbital state and confirm the electrochemically measured stability following the sequence [EMIM][B(CN)4] > [EMIM][N(CN)2] > [EMIM][C(CN)3].