Surface science tools requiring ultrahigh vacuum (UHV) conditions, such as X-ray photoelectron spectroscopy (XPS), are applicable due to the intrinsically low vapour pressure of ILs. Using ILs as electrolytes to study electrochemical processes at the solid -liquid interface allows studying processes at po-tentials beyond the stability window of water (1.23 V). However, it was also shown that impurities can have a significant impact on the electrochemical properties. 9,10 A common approach to studying such systems is cyclic voltammetry, where a current is recorded upon applying a triangular wave potential. The features in the current signal are a fingerprint of the investigated system, as shown extensively for aqueous electrochemical systems. In turn, when the electrode's quality is wellknown, possible changes in the electrolyte can be deduced, thus, making the electrode a sort of probe.