Thus, to illustrate the role of water on the peaks observed in the CVs more profoundly, we added water to the IL and monitored the evolution of the electrochemical properties with time. For the following example, the water content of an IL was increased from 75 ppm to around 450 ppm. After storing the IL for five days in a closed container in a N 2 -flooded glovebox, the amount of water was still 450 ppm. Interestingly, the CVs for Au(111) recorded in the IL containing additional water after 12 h, 2 days, and 5 days, which are shown in Figure , changed significantly. Here the first cycles are shown inFigure 4a and the fifths cycles in 4b with solid lines. For comparison, the CVs for Au(111) recorded in the as-received IL with a water content of approximately 75 ppm are shown with dashed lines. In the first measurement 12 h after the water addition, the first cycle (Figure ) shows a significant increase of peak C1 and a decrease of peak C3. At the same time, the positive-going scan does not show any significant changes. With longer storage times peak C1 in the first cycle (Figure ) decreases for the IL with an initial water content of 450 ppm. After five days, the CV appears almost similar to that recorded in the as-received IL with a water content of 75 ppm. After five potential cycles, all CVs look almost identical except for that, which had an initial water content of 450 ppm and stored for 12 hours (Figure ). Hence, since the water content did not change over five days, water cannot be at the origin of the changes observed in the CVs after the different measurements. This means that a species that is either volatile or decomposed with time was introduced along with the water into the IL. Based on our previous works with aqueous electrolytes, we are confident that the ultrapure water added to the IL was free from metal or hydrocarbon impurities. The nondeaerated water was, however, added to the IL under ambient atmosphere. The vial was evacuated of atmospheric gas before its transfer into the glove box. We suggest that O 2 dissolved in the IL is not removed by this treatment. Hence, peak C1 is possibly related to O 2 reduction. During the storage in the glove box, the amount of dissolved O 2 decreases with time, due to diffusion into the glove box atmosphere, which hasO 2 contents lower than 0.5 ppm. A more detailed reasoning to attribute peak C1 to O 2 and possible reaction mechanisms for the reduction of O 2 on the Au(111) electrode in the presence and absence of water is discussed elsewhere.