The Center for Interfacial Ionics aims to establish principles and predictive models for IIT that broadly enable the rational design of advanced electrochemical systems for societally important applications such as using electrical energy to drive selective and efficient chemical transformations. The Center has made substantial fundamental advances across several synergistic lines of investigation.

Model Studies of IIT at Liquid|Liquid Interfaces

The chemical heterogeneity inherent to most solid electrode surfaces impedes fundamental understanding of structure-function relationships in IIT. We have addressed this challenge by investigating IIT at the “defect-free” interfaces between two immiscible liquids. We have quantified rates of interfacial proton transfer across liquid|liquid interfaces using nanopipette voltammetry and uncovered the mechanistic basis for direct versus sequential proton transfer across the interface. These studies provide a molecular lens into interfacial proton transfer reactions that informs studies of more complex reactions across the Center.

IIT at Molecularly Precise Solid|Liquid Interfaces

To overcome the challenge of surface heterogeneity for IIT at solid|liquid interfaces, the Center has investigated interfacial proton transfer reactions to carbon surfaces conjugated to molecularly well-defined acid/base moieties. These graphite-conjugated acid sites provide a rich platform for uncovering molecularly level insights into IIT. Through these studies, the Center has found that interfacial proton transfer (IPT) reactions do not proceed as a single elementary reaction step, as previously thought. Instead, the elementary IPT reaction is gated by the formation of a pre-association complex with the surface active site, which involves substitution of electrolyte ions with reactive proton donor/acceptors. These findings have broad implications for the rational design of fast IIT process. Leveraging these insights, the Center is developing strategies for catalyzing IIT reactions.

Exposing the Role of IIT in Thermal Catalysis

Typically, IIT reactions are studied as part of Faradaic processes, but they can also play a key role in non-Faradaic thermochemical catalysis. With this notion in mind, the Center investigated the role of IIT in the context of Pd-catalyzed vinyl acetate synthesis. Vinyl acetate is an industrially important product produced via the gas-phase aerobic oxidation of ethylene and acetic acid over Pd catalysts. The Center discovered that vinyl acetate synthesis can proceed via the aerobic IIT corrosion of Pd to Pd(II) ions, and subsequent acetoxylation of ethylene by Pd(II) to generate vinyl acetate and re-deposit Pd metal. Kinetic studies indicate that the IIT reaction step of metal corrosion limits the rate of this overall thermochemical catalytic reaction. These studies highlight the central role of IIT reactions in thermochemical catalysis and illustrate how IIT can enable fundamentally new mechanistic paradigms that leverage complementarity between molecular and surface active sites. These studies emphasize the need for a deep mechanistic understanding of IIT reactions across diverse contexts.