It appears as if the H 2 formed at the plasma counter electrode has an effect on the amount of H 2 O 2 in the solution. The reason for this behavior remains, however, unknown. S6: Temporal evolution of cyclic voltammograms after aCGDE Fig. shows the first and second cycles of the CVs recorded at a Pt AE directly after aCGDE (580 V for 30 s). For an AE placed at a distance of 4.5 cm from the PWE, in the first cycle (blue curve) a reduction peak is observed at around 0.6 V RHE in the negative going scan (see manuscript). In the second cycle (light blue curve) the reduction peak is smaller and the maximum is located at 0.8 V RHE , hence at a similar potential than what is observed in a CV recorded before the experiment (black curve). The current densities related to ORR (additional negative current density) also decreased significantly in the second scan. Placing the electrode at 1.5 cm from the PWE, a large positive current density is observed in the first negative going scan at potentials > 0.65 V RHE (red curve). In the second cycle, the positive current density associated with the hydrogen peroxide reduction is much lower, but still measurable. Overall the CV is slightly shifted to more negative current densities for potentials < 0.65 V compared to the CV recorded before the experiment (black curve), which can be explained by the reduction of O 2 and H 2 O 2 at the Pt electrode. In the first cycle (red curve), the CV is not as much shifted to lower current densities than in the second cycle (pink curve). This might be caused by an initially large H 2 concentration in the solution, which reacts with the Pt electrode giving rise to a positive current density which overlaps with negative current densities for ORR and HPRR. More importantly, a positive current density is still apparent at potentials > .95 V RHE . This indicates that H 2 O 2 is still present in the solution, which is oxidized at these potentials. The concentration is, however, much lower compared to the first cycle.