Proton-Transfer Kinetics at Liquid-Liquid Interfaces

Area of Science:

• Electrochemistry
• Physical Chemistry
• Chemical Engineering

Background:

• Proton transfer is crucial for electrochemical processes but difficult to measure at electrode interfaces.
• Existing methods are complicated by electron transfer and surface defects.
• The interface between two immiscible electrolyte solutions (ITIES) offers a simplified system.

Purpose of the Study:

• To investigate proton transfer kinetics at the ITIES, free from electron transfer and surface irregularities.
• To establish a model system for studying fundamental proton transfer mechanisms.
• To determine kinetic parameters for facilitated proton transfer.

Main Methods:

• Utilized diffusion-controlled micropipette voltammetry and nanopipette-supported interfaces.
• Employed a mixed diffusive-kinetic model to analyze voltammograms.
• Performed finite-element and atomistic molecular-dynamics simulations.

Main Results:

• 2,6-diphenylpyridine (DPP) was identified as a facilitator for proton transfer across the HCl(aq)|trifluorotoluene interface.
• Apparent kinetic parameters (k°app = 3.0 ± 1.8 cm/s, αapp = 0.3 ± 0.2) were extracted.
• Simulations indicated a preference for direct proton transfer when DPP partitioning was rate-limiting.
• Molecular dynamics predicted proton transfer occurs in the interpenetrating liquid surface region.

Conclusions:

• The ITIES platform provides a robust method for studying intrinsic proton transfer kinetics.
• Understanding ion transfer at ITIES contributes to broader theories in electrochemical science.
• This research offers insights into facilitated proton transfer mechanisms and interfacial phenomena.