Assessing the Quality of Ionic Liquids Using Single Crystal Electrochemistry, Surface Science and Data Screening

Ionic liquids (ILs) are used in numerous chemical, biological, and physico-chemical applications. Native impurities in the IL, however, often limit the interpretation of results or the applicability of these chemicals. Here, we present an electrochemical approach, where the quality of ILs is visualised with cyclic voltammetry using well-defined single-crystal electrodes. As an example, we study Au(111) in N-methyl-N-propylpiperidinium bis(trifluoromethane)sulfonimide ([MPPip][TFSI]), where different suppliers with different supplied purity and different pretreatments are considered. The importance of studying the quality of ILs after pretreatments is illustrated with additional X-ray photoelectron spectroscopy measurements. We also show that the storage conditions and time/age can have a significant impact on the amount of water and oxygen in the IL. The relevance of reporting metadata and the role of databases in elucidating benchmark systems is also discussed.