Research Overview
A unifying theme of our research program is the pursuit of fundamental chemical understanding through the use of optical, electrical, and magnetic external fields to measure, drive, and control interfacial chemical transformations at the nanoscale. At its core, our work seeks to elucidate the physical chemistry governing the interconversion of chemical and electrical energy in electrocatalytic systems. We pursue this objective through two complementary strategies: (1) controlling the local microenvironment at the electrode–electrolyte interface to enhance activity and selectivity, and (2) developing and applying high-resolution optical microscopy and spectroscopy to reduce ensemble averaging in electrocatalysis and directly measure surface species and reaction intermediates. These approaches emphasize mechanistic understanding and aim to provide generalizable principles that can be leveraged to design more efficient and selective catalysts for fuel generation and consumption reactions, as well as small-molecule transformations relevant to energy and organic synthesis.
Nanomaterials
Image credit: Dr. Ki-Hyun Cho
As materials shrink to the nanoscale, their surface area-to-volume ratios increase dramatically, and quantum mechanical effects begin to dominate their behavior. These size-dependent phenomena fundamentally alter chemical reactivity as well as the optical, electrical, magnetic, and mechanical properties of materials. A classic example is gold: while bulk gold appears yellow, suspensions of gold nanoparticles exhibit colors spanning the visible and near-infrared regions of the electromagnetic spectrum, depending on their size, shape, and composition. Our research focuses on the bottom-up synthesis and top-down fabrication of nanomaterials with precisely controlled size, morphology, and composition to tailor their properties for applications in molecular sensing and chemical catalysis. Beyond serving as functional materials, nanostructures provide powerful platforms for engineering thin films and surfaces and for enhancing spectroscopic signals, enabling the study of molecules and materials under dynamic operating conditions. Our laboratory investigates a broad range of transition metal and metal oxide nanomaterials, including nanoparticles (spheres, rods, cubes, hollow structures, alloys, bimetallic, and core-shell architectures), nanoparticle arrays, nanowires, and thin films.
Electrocatalysis
Nanoparticle image credit: Dr. Varun Mohan
A major challenge in building a sustainable energy economy is the efficient storage, conversion, and utilization of renewable energy. Electrochemistry is uniquely positioned to address this challenge by enabling the storage and release of energy through chemical bonds while integrating with electricity generated from renewable sources such as solar and wind. Our research leverages abundant small molecules (e.g., nitrogen, oxygen, water, and carbon dioxide) and earth-abundant transition metals to develop electrochemical technologies for fuel production, value-added chemical synthesis, fuel cells, and metal-air batteries. Achieving these goals requires electrocatalysts that are highly active, selective, and stable under operating conditions. A central strategy in catalyst design is tuning the electronic structure of catalytic materials to optimize reaction energetics. However, for many complex multi-electron, multi-proton reactions, catalyst performance is fundamentally constrained by adsorbate scaling relationships, which limit simultaneous optimization of reaction intermediates. To overcome these limitations, our laboratory combines traditional electrocatalyst engineering with emerging strategies that use external stimuli (e.g., optical and magnetic fields) to dynamically manipulate catalytic processes. By controlling the catalyst microenvironment and reaction pathways beyond conventional materials design, we seek to break scaling relationships and enable transformative advances in the efficiency, selectivity, and sustainability of electrochemical energy conversion.
Spectroscopy/microscopy
Chemical reactions are traditionally studied and optimized using ensemble measurements in the proverbial beaker. While these experiments reveal average reaction rates, mechanisms, and trends, they often obscure the heterogeneity that exists at the nanoscale, where every molecule, nanoparticle, and catalytic site experiences a distinct local environment. Understanding how these local environments govern chemical reactivity and establish structure–function relationships requires measurements with single-particle, single-site, and single-molecule sensitivity. Our research advances analytical measurements at the limits of spatial, temporal, and energy resolution by developing and integrating spectroscopic and microscopic techniques that reveal chemical processes hidden within ensemble averages. By combining spectroscopy with high-resolution imaging, we directly observe the dynamic behavior of molecules and materials during chemical transformations. Our work spans a broad range of optical techniques, including surface-enhanced Raman spectroscopy (SERS), fluorescence microscopy, infrared spectroscopy, and super-resolution imaging. We are particularly interested in applying these methods to uncover the mechanisms of interfacial chemical transformations, providing fundamental insights that guide the design of next-generation catalysts, functional materials, and sensing platforms.