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

Abstract

Dedicated to Prof. Hubert Girault on the occasion of his 65 th birthdayBiphasic interfacial electron transfer (IET) reactions at polarisable liquid j liquid (L j 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 D w o � 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 j L interface. We outline that the applied D w o � 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 j L interface simultaneously in order to react.

Potential-Modulated Surface-Enhanced Raman Spectroscopy of Tolmetin at Gold Nanoparticle Film Functionalized Polarizable Liquid–Liquid Interfaces

“…The distinct physicochemical conditions at a polarized liquid–liquid interface, compared to the bulk aqueous phase, may also favor the formation of this coral reef structures. For example, the positive OCP set by the LiTB electrolyte enhances the concentration of Na + cations in the electrical double layer on the aqueous side of the liquid–liquid interface by an order of magnitude at least . This significant local increase in the aqueous cation concentration may diminish the distance between both AuNPs and their aggregates by further neutralizing the anionic electrostatic repulsive forces and, thereby, favor the fusion of AuNPs with existing aggregates present at the liquid–liquid interface.…”

“…For example, the positive OCP set by the LiTB electrolyte enhances the concentration of Na + cations in the electrical double layer on the aqueous side of the liquid–liquid interface by an order of magnitude at least. 34 This significant local increase in the aqueous cation concentration may diminish the distance between both AuNPs and their aggregates by further neutralizing the anionic electrostatic repulsive forces and, thereby, favor the fusion of AuNPs with existing aggregates present at the liquid–liquid interface. Conversely, the negative OCP set by the BACl electrolyte enhances the concentration of Cl – anions in the electrical double layer on the aqueous side of the liquid–liquid interface, potentially increasing the inter-AuNP distances and, thereby, inhibiting the fusion of AuNPs with existing aggregates.…”

“…In this work, polarizing salts that establish open-circuit potentials (OCPs) at Δ o w ϕ values at the positive and negative extremes of the polarizable potential window (PPW) are investigated, and their influence on the SERS signal compared to that under OCP conditions established by a salt containing both a hydrophobic cation and an anion (neither of which partition out of the organic phase within the PPW). Polarization of the liquid–liquid interface influences the ion distributions in the electrical double-layers on both sides of the interface, which in turn influences the morphology of the interfacial AuNP films formed and, thus, the nature of the SERS signal recorded. Additionally, polarization of the liquid–liquid interface can influence the SERS signal by enriching or depleting the concentration of the analyte (if it is ionic in nature) in the interfacial region or lead to the formation of interfacial ion pairs between the ionic analyte and oppositely charged electrolyte ion in the adjacent phase, e.g., the formation of an ion pair between an anionic aqueous analyte and the organic electrolyte cation.…”

Design of Single‐Atom Catalysts for E lectrocatalytic Nitrogen Fixation

“…At present, solid oxide electrolytic cells and H-type electrolytic cells are mainly used.. [28] They can control the proton source to suppress the HER response. [33] Considering the low solubility of N 2 in water, Wang et al used proton-conducting solid oxide electrolysis cells (PCECs) to transport protons, and they obtained oxygen vacancy-rich perovskite catalysts by using iron doping. The results showed that the catalytic system based on PCECs exhibited a highly efficient electrocatalytic ability to synthesize ammonia (NH 3 yield was 6.84×10 À 9 mol cm À 2 s À 1 and FE was 2.79 %).…”

“… [28] . They can control the proton source to suppress the HER response [33] . Considering the low solubility of N 2 in water, Wang et al.…”