The charge transfer processes across the interface between two immiscible electrolyte solutions (ITIES) can be employed for energy storage and conversion, solvent extraction, or sensing or in life sciences. Among them are catalytic reactions, which have only been recently studied. Here H 2 O 2 generation is studied with decamethylferrocene (DMFc) as electron donor at the interface between tetrahexylammonium perchlorate solution in 1,2-dichloroethane (1,2-DCE) and aqueous HClO 4 . These conditions are unfavorable for proton transfer across ITIES because of positive Galvani potential difference. Voltammetry with 1,2-DCE droplet modified electrode shows that DMFc oxidation is accompanied by ClO 4 − insertion into the organic phase. The reaction progress was followed by UV−vis spectroscopy, voltammetry, and scanning electrochemical microscopy (SECM). In the first and last method, horseradish peroxidase was used as catalyst. It is concluded that O 2 is reduced to H 2 O 2 at the liquid|liquid interface not only under conditions when proton transfer to organic phase is strongly favored, namely, when Galvani potential difference is negative (Angew. Chem., Int. Ed. 2008, 47, 4675−4678).