Catalytic Activity of Alkali Metal Cations for the Chemical Oxygen Reduction Reaction in a Biphasic Liquid System Probed by Scanning Electrochemical Microscopy

• Published in: Chemistry : a European journal Vol. 26; no. 47; pp. 10882 - 10890
• Main Authors: Rastgar, Shokoufeh, Teixeira Santos, Keyla, Angelucci, Camilo Andrea, Wittstock, Gunther
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 21.08.2020; John Wiley and Sons Inc
• Subjects: Acidity; Alkali metals; Aqueous electrolytes; biphasic catalysis; Catalytic activity; Cations; chemical oxygen reduction reaction; Chemical reduction; Chemistry; Dichloroethane; Electrochemistry; Electrolytes; Fluxes; hydrated alkali ions; Hydrogen peroxide; ion transfer voltammetry; Ions; Metal ions; Microelectrodes; Nonaqueous electrolytes; Organic solvents; Orifices; Oxidation; Oxygen; Oxygen reduction reactions; phase-transfer catalysis; Reactive oxygen species; Reagents; Scanning; Substrates; ion transfer voltammetry; hydrated alkali ions; electrochemistry; phase-transfer catalysis; biphasic catalysis; chemical oxygen reduction reaction
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202001967

Chemical reduction of dioxygen in organic solvents for the production of reactive oxygen species or the concomitant oxidation of organic substrates can be enhanced by the separation of products and educts in biphasic liquid systems. Here, the coupled electron and ion transfer processes is studied as well as reagent fluxes across the liquid|liquid interface for the chemical reduction of dioxygen by decamethylferrocene (DMFc) in a dichloroethane‐based organic electrolyte forming an interface with an aqueous electrolyte containing alkali metal ions. This interface is stabilized at the orifice of a pipette, across which a Galvani potential difference is externally applied and precisely adjusted to enforce the transfer of different alkali metal ions from the aqueous to the organic electrolyte. The oxygen reduction is followed by H2O2 detection in the aqueous phase close to the interface by a microelectrode of a scanning electrochemical microscope (SECM). The results prove a strong catalytic effect of hydrated alkali metal ions on the formation rate of H2O2, which varies systematically with the acidity of the transferred alkali metal ions in the organic phase. At the interface: Oxygen reduction by decamethylferrocene close to an interface between an aqueous and organic electrolyte solution is catalyzed by hydrated alkali metal cations in the order K+<Na+<Li+ being transferred from the aqueous to the organic phase by a suitable potential across the liquid|liquid interface. The reaction was followed by amperometric product detection in the aqueous phase.