Dynamics at Electrode-Electrolyte Interfaces Down to the Nanosecond Domain

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This project is jointly funded by the Chemical Measurement and Imaging Program and the Chemical Structure, Dynamics and Mechanisms - A Program. Both are in the Division of Chemistry. Professor Daniel Scherson of Case Western Reserve University is developing and using hardware and electroanalytical methods for ultrafast charge injection across electrode/electrolyte interfaces. This capability enables fundamental studies of electrochemical phenomena at timescales down to the nanosecond (ns) regime. These new ultrafast electronics are combined with spectroscopic techniques such as second harmonic generation (SHG), sum frequency generation (SFG), and differential reflectance spectroscopy. This work will provide the means to answer fundamental questions about the dynamics of short-lived adsorbates and reactive intermediates. The behavior of electrode and electrolyte interfaces are highly relevant to a wide-range of electrochemical applications. Electrochemical surface science lies at the juncture of chemistry, physics and a wide number of engineering fields, such as materials and electronics. The scientific advances will impact wide ranging areas of practical importance such as energy conversion, corrosion mitigation and sensor technology. Students pursuing research in this area become exposed to a very broad range of both fundamental and applied disciplines. This type of training will produce students especially suited to face the challenges posed by a multitude of important and unresolved problems in environmental remediation, energy conversion, energy storage, biosciences, and microsensor technology. The primary objectives of this work are to develop and implement experimental techniques to achieve potential control across electrode/electrolyte interfaces in the nanosecond regime, and to monitor the subsequent time evolution of the interface using spectroscopic techniques with the highest sensitivity and specificity and temporal resolution. Attention is focused on ultrafast charge injection tactics employing electronic circuitry and electrochemical cell architectures designed in collaboration with Tektronix (Keithley). These is validated using selected model systems involving both well-defined single crystal metal substrates and adsorbate layers. The response of the systems to such fast electrical perturbations is monitored using linear and non-linear spectroscopic probes, including normalized differential reflectance, and second harmonic, (SHG) and sum frequency generation (SFG). The actual model systems investigated include: electron transfer in self-assembled monolayers bearing redox active terminal groups as a function of the distance from the electrode surface, order/disorder transitions in halide adsorbate layers on single crystal silver, and hydrogen adsorption/desorption on Pt(111) as a function of pH. Also explored is the use of ultrafast current pulses applied to the solution in order to modulate the electrostatic potential across the interface and thus the overpotential driving the interfacial events. It is expected that the experimental data resulting from this research will serve to validate theoretical predictions emerging from the fast developing field of interfacial dynamics.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.