Proton Transfer Kinetics at a Defect-Free Liquid-Liquid Interface

Proton transfer at electrochemical interfaces is fundamentally important for many areas of science and technology, yet kinetic measurements of this elementary step are often convoluted by inhomogeneous electrode surface structures. We show that facilitated proton transfer at the interface between two immiscible electrolyte solutions (ITIES) can serve as a model system to study proton transfer kinetics in the absence of defects found at solid|electrolyte interfaces. Diffusion-controlled micropipette voltammetry revealed that 2,6-diphenylpyridine (DPP) facilitated direct proton transfer across the liquid|liquid interface and voltammetry at nanopipette-supported interfaces yielded activation-controlled ion transfer currents. The exchange current density for proton transfer at the ITIES is comparable to exchange current densities recently reported for H-UPD on Pt (111) and provides the first direct means of comparing ion transfer kinetics between solid|liquid and liquid|liquid interfaces, supporting the development of a general theory of ion transfer kinetics.