A common theme in our research is using light‒matter interactions and electrical energy to measure, drive, and control interfacial chemical transformations at the nanoscale. In particular, we are interested in advancing our fundamental understanding of the interconversion of chemical and electrical energy. Our approach is to develop and employ high resolution optical microscopy and spectroscopy to investigate electrochemical processes beyond the ensemble, at the single particle, single molecule level. We aim to gain and leverage mechanistic insight in chemical reactions to achieve high efficiency and selectivity in fuel generation/consumption reactions and increase the performance of high-capacity, rechargeable batteries. Below are brief descriptions of current research areas.
Image credit: Dr. Ki-Hyun Cho
As materials decrease in size, their surface area to volume ratios increase and their attributes are increasingly described by quantum mechanical effects. These characteristics lead to changes in chemical reactivity as well as a material’s optical, electrical, magnetic, and mechanical properties. A classic example is that the color of bulk gold is yellow, yet the color of solutions of gold nanoparticles can span across the visible spectrum and into the near-infrared spectrum. We synthesize (bottom-up) and fabricate (top-down) nanomaterials of different size, morphology, and composition to tune their properties for applications in molecular sensing and chemical catalysis. Additionally, nanomaterials aid our research by allowing us to engineer thin films and surfaces as well as enhance spectroscopic signals from molecules and materials in dynamic systems. Examples of materials used in our lab include transition metals and metal oxides. Structures include nanoparticles (spheres, rods, cubes, hollow structures, alloys, bimetallics, core-shell structures), arrays of nanoparticles, nanowires, and thin films.
Nanoparticle image credit: Varun Mohan
A critical challenge in the realization of a sustainable energy economy is the effective storage, redistribution, and use of clean energy from renewable sources. Electrochemistry is aptly suited to help achieve this goal because it facilitates the storage and release of electrons in chemical bonds and is compatible with the electrical output from renewable sources. We aim to use molecules widely available in the environment (e.g. nitrogen, oxygen, water, carbon dioxide) and earth-abundant metals (e.g. first row transition metals) for the electrochemical synthesis of fuels (and organic molecules more generally), fuel cells, and metal-air batteries. Central to advancements in these electrochemical processes is the development of stable, active electrocatalysts that facilitate chemical transformations with high selectivity. An effective approach in electrocatalyst design is tuning the electronic structure of the catalyst. However, this approach is limited in multi-proton, multi-electron reactions by adsorbate scaling relations. Thus, complementary to electrocatalyst engineering, we are developing new approaches to overcome scaling relations to enable high efficiency and selectivity in electrocatalysis.
Reaction rates, reaction mechanisms, and experimental parameters of chemical transformations are often measured and optimized in the proverbial beaker. At this scale, ensemble measurements can assess general trends, but within the beaker, each molecule, particle, and surface experiences a unique environment. To understand how local, nanoscale environments influence chemical reactivity and the structure-function relationships between phases of matter, measurements of single particles, single sites, and single molecules are necessary. We are pushing the boundaries of analytical detection in space, time, and energy by developing tools and strategies that merge spectroscopy with microscopy to uncover the action of molecules and materials hidden by statistical ensemble measurements. Some of the techniques include but are not limited to surface-enhanced spectroscopy, Raman scattering, Brillouin scattering, fluorescence, infrared spectroscopy, and super-resolution imaging. We are particularly interested in developing and applying high resolution measurements to study the mechanisms of chemical transformations at interfaces.