However, commonly water is already present in the as-received ILs, and thus has to be removed carefully. Approaches to reduce the amount of water in the ILs used in the present work have been suggested previously, which involve drying and heating in vacuum followed by treating the IL with a molecular sieve. Our results confirm that using heating and vacuum alone, has no significant impact on the electrochemical properties, even though the water content decreases. Regarding the addition of a molecular sieve, there exist contradictory conclusions on the most suitable pore size (3 A 41 vs. 4 A 31 -used in this work and Ref. 31). We assume that the ability to remove water also depends on the batch and supplier of the molecular sieve. A former study shows a contamination from Na from the molecular sieve. In our measurements, we observed additional peaks in the CVs when a molecular sieve was involved in the drying process. Specifically, we assume that these peaks are related to Na, based on the positions of the peaks in the CV, which are similar to those noted during Na deposition on Au(111) from the same IL in a previous work. Whether or not a possible contamination depends on the type, supplier or batch of the particular molecular sieve requires further experimental studies. Finally, by using the molecular sieve we also observe a decrease of peak A1 in all cases (Figure ). To this point, it remains unclear as to why peak A1 decreases, but it is likely that a certain impurity is indeed removed to some extent by the molecular sieve treatment, which has an impact on the process taking place in this potential region (see below). For the same reason, it is likely that the peaks C2 and A2 in type II vanish with the addition of a molecular sieve. The processes which lead to these peaks could be induced or catalysed by impurities which are removed by the molecular sieve.