For the interpretation of our results, we suggest that the reaction of residual O 2 with H 2 O is the dominant reaction pathway. Depending on the batch of electrolytes, these processes occur in type I in peak C1 and in type II in peaks C1 and C2. According to Katayama et al. possible products formed within these peaks are reoxidized in the subsequent positive-going scan for type I in peak A1 and for type II in peaks A2 and A1. Considering that the catalytic reaction (no charge transfer) in Equation (suggested by Katayama et al.) takes place, it is expected that the reduction peaks are larger than the oxidation peaks. This is indeed the case in our experiments and is apparent by the high charge passed in the cathodic current regime compared to the anodic current regime (see table 2). Interestingly, the size of peak A1 in the positive-going scan decreases only slightly, while peak C1 in the negative-going scan decreases significantly, when O 2 is consumed during continuous potential cycling or removed over time from the electrolyte. Thus, the peak must be related to a specific reaction. We suggest that peak A1 is related to the oxidation of OH -. To verify this assumption, we recorded CVs in [MPPip][TFSI] (type I, batch 3) containing 0.4 M H[TFSI], which is shown in the SI (Figure ). The addition of H[TFSI] significantly reduces the size of peak A1, which is possibly caused by a decrease of the OH -concentration due to the recombination with the H + ions. Another explanation is the reaction of H + ions with O 2 to form hydrogen peroxide as proposed by Switzer et al. and Yuan et al. and given in equation 7. This reaction contributes to the charge during the negative-going scan, but since no OH -is formed, the charge in peak A1 is smaller.