Photoelectrokinetic Spectroscopy: A New Probe of Solid/Liquid Interfaces

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With support from the Chemical Measurement and Imaging Program in the Division of Chemistry, Prof. Richard Saykally and his group at the University of California - Berkeley are investigating a novel concept for measuring the spectroscopic properties of aqueous interfaces, with long-term aims of developing new instruments and devices, as well as an enhanced understanding of the basic nature of electrolyte interfaces. Microfabricated channels of selected materials (e.g. glass, silicon, with various coatings) with suitable optical windows are connected to a liquid chromatography system which delivers liquids with precisely controlled composition, pressure, and flow through the channel. The resulting electrokinetic current/voltage is monitored both upstream and downstream from a nozzle exit orifice. The magnitudes of these observables depend explicitly on the properties of the solid/liquid interface (zeta potential, ion and electron mobilities, charge transfer cross sections, electric field). When light impinges on the liquid/solid interface, changes induced in the electrokinetic current and potential are observed. Measuring the changes in these quantities as a function of the optical wavelength and power can produce a spectrum of the chromophores localized in the interfacial region (adsorbed to the solid or located in the double layer). This new approach can help characterize the nature of electrolyte interfaces, providing information essential for advancing the crucial technologies of batteries, fuel cells, solar fuel generators, and photovoltaics. In addition to this potentially transformative scientific impact, the work is providing training in the development of new methods and instrumentation.