Reproducibility of electrochemical measurements with ionic liquids: Is the water content the decisive parameter?

Studying the potential dependent interaction of non-aqueous electrolytes, such as ionic liquids (ILs), with model electrode surfaces plays a crucial role not only in the field of battery-related research. These electrolytes bear the advantage that their electrochemical stability windows often exceed that of water. Comparing results using ILs as electrolytes reported in the literature reveals strong discrepancies in the reproducibility of the data. In this study, we show that parameters such as the supplier, the supplied batch, and the purification steps can have a huge impact on the electrochemical properties. As a reference system, these properties are studied by cyclic voltammetry on a Au(111) single crystal electrode in N-methyl-N-propylpiperidinium bis(trifluoromethane)sulfonimide ([MPPip][TFSI]). Analysing the different features observed in the cyclic voltammograms, we were able to deconvolute (to some extent) the features that are related to the interaction of ILs with the substrate, impurities added from the pre-treatment due to the influence of residual water and oxygen.