Potential-Modulated Ion Distributions in the Back-to-Back Electrical Double Layers at a Polarised Liquid|Liquid Interface Regulate the Kinetics of Interfacial Electron Transfer

Biphasic interfacial electron transfer (IET) reactions at polarisable liquid|liquid (L|L) interfaces underpin new approaches to electrosynthesis, redox electrocatalysis, bioelectrochemistry and artificial photosynthesis. Herein, using cyclic and alternating current voltammetry, we demonstrate that under certain experimental conditions, the biphasic 2-electron O-2 reduction reaction can proceed by single-step IET between a reductant in the organic phase, decamethylferrocene, and interfacial protons in the presence of O-2. Using this biphasic system, we demonstrate that the applied interfacial Galvani potential difference Delta ow phi ${{\Delta }_{{\rm o}}<^>{{\rm w}}\phi{} }$ provides no direct driving force to realise a thermodynamically uphill biphasic IET reaction in the mixed solvent region. We show that the onset potential for a biphasic single-step IET reaction does not correlate with the thermodynamically predicted standard Galvani IET potential and is instead closely correlated with the potential of zero charge at a polarised L|L interface. We outline that the applied Delta ow phi ${{\Delta }_{{\rm o}}<^>{{\rm w}}\phi{} }$ required to modulate the interfacial ion distributions, and thus kinetics of IET, must be optimised to ensure that the aqueous and organic redox species are present in substantial concentrations at the L|L interface simultaneously in order to react.

Automated summary

Biphasic interfacial electron transfer (IET) reactions at polarisable liquid|liquid (L|L) interfaces play crucial roles in various applications such as electrosynthesis and bioelectrochemistry. In this study, we demonstrate the occurrence of biphasic 2-electron O-2 reduction reaction through single-step IET between decamethylferrocene and interfacial protons. The interfacial Galvani potential difference was found to have no direct driving force for the biphasic IET reaction, and the correlation between the onset potential and the potential of zero charge at the polarised L|L interface was identified. The optimization of interfacial ion distributions is important for achieving substantial concentrations of aqueous and organic redox species at the L|L interface simultaneously.