Surface Chemistry and Catalysis
Our research group examines reactions at and with surfaces in an effort to develop new types of heterogeneous catalysts. We use an on-surface metal-ligand coordination strategy to stabilize single-atom catalysts. These have well-defined structure and chemical function.
Student and postdoctoral researchers in our lab synthesis catalysts, characterize them with a suite of analysis tools, and examine their activity for selective chemical transformations.
Part of this research effort is done under pristine and highly-controlled ultra-high vacuum environments. These environments allow us to precisely control the surface composition and examine structure with single molecule resolution using scanning tunneling microscopy and chemical transformations using photoelectron spectroscopy and vibrational spectroscopy. These experiments provide fundamental insights into redox chemistry at surfaces and benefit greatly from collaborations with other groups.
The other major part of this research effort is to develop single-atom catalysts using the metal-ligand strategy on high surface area oxide supports. These experiments are done under ambient conditions. Catalysts are synthesized in solution, then loaded into either a batch reactor or a flow reactor to examine their performance. We characterize the catalysts using ex situ techniques, including X-ray photoelectron spectroscopy, electron microscopy, inductively-coupled plasma mass spectrometry, and other techniques. We also use both in situ and ex situ X-ray absorption spectroscopy tools at Argonne National Laboratory to examine the catalysts.
All of these experiments fit together to help advance new types of catalysts to address critical energy problems around the world.
Our group has an exciting fundamental research program to examine spontaneous supramolecular self-assembly at surfaces. These experiments are aimed at developing novel materials using a “bottom-up” approach, i.e., careful design of simple molecular building blocks allows programming of structure and function in self-organized molecular materials. Our group collaborates closely with several research groups for the design and synthesis of families of related molecules. By examining the molecules in sets, we can evaluate how specific modifications to the building blocks impact the final structure and functions of the molecular layers or films.
Student researchers on this project design experiments in a range of concentrations and molecule deposition conditions, then examine molecular assemblies at surfaces using scanning tunneling microscopy for molecular resolution imaging and other techniques. Some of these experiments are conducted in ambient conditions by molecular deposition from solution (controlling concentration, solvent, and temperature). Other experiments are conducted by vapor deposition of the molecules to the surface under vacuum conditions (controlling surface composition, deposition rate, and temperature).
These experiments provide insight into fundamental physical and chemical interactions that drive self-assembled, functional organic surface structures. We are particularly interested in developing robust and highly-ordered architectures that will impact advances in organic photovoltaics and molecular electronics. Excellent ordering is important for each of these applications. Highly-ordered organic layers at surfaces offer significant improvement in charge transfer and device efficiency compared to less-ordered polymer films.