Professor of Chemistry, Program in Applied Physics, Associate Chair for Climate & Culture
About
Heterogeneous charge transfer is at the heart of microelectronics, many chemical sensing strategies, and energy conversion/storage technologies. Understanding, designing, and developing more efficient electrode surfaces for systems based on interfacial charge transfer are my group's research interests. Advancements in these fields requires further understanding of, and control over, the kinetics of charge transfer, stability of the interface, and material properties of the system components.
Our group is particularly interested in developing solar energy conversion and storage systems. For any system to be capable of converting sunlight into chemical energy (i.e. chemical bonds), sunlight must be efficiently absorbed, photoexcited electrons and holes must be generated, and these charge carriers must be separately directed to reaction sites where they can drive redox reactions. Inorganic semiconductors are naturally suited for all three of these required tasks. In fact, a semiconductor electrode in contact with a liquid solution is arguably the simplest design for an artificial, solar-powered fuel generator. Inorganic semiconductors strongly absorb photons with energies greater than the band gap, support energetically and spatially separated electrons and holes, and are natural platforms for heterogeneous electron transfer. However, the difficulties associated with simultaneously maximizing the absorption of sunlight, optimizing the thermodynamics and kinetics for interfacial charge transfer, and preserving the longevity of the semiconductor/solution interface have stalled development of such photoelectrochemical systems. Deliberate and systematic control over the electrical, physical, and electrochemical properties of the surfaces of inorganic semiconductors would greatly improve the viability of such photoelectrochemical systems.
Available research projects in the group involve studying and optimizing semiconductor interfaces for solar energy conversion and storage. One main focus is to chemically protect inorganic semiconductor surfaces (e.g. Si, GaP) with various organic functional groups and to use linking chemistries to attach electrocatalytic materials to these surfaces. The motivation is to design systems where charge-transfer reactions can be modulated and understood. A separate interest in the lab is the electrochemical synthesis of inorganic crystalline materials. Our group invented the electrochemical liquid-liquid-solid process, a tactic that uses an electrochemical gradient rather than a thermal gradient to drive crystal formation. This approach can lead to the green synthesis of foundational semiconductor materials (e.g. Si, Ge, GaAs) at record low temperatures and to the discovery of entirely new compositions of matter.
These projects will rely heavily on surface sensitive analytical techniques (e.g. x-ray photoelectron spectroscopy, scanning probe microscopies), materials characterization methods (e.g. transmission electron microscopy, scanning electron microscopy), optical studies (e.g. infrared spectroscopy, uv-vis spectroscopy), and electroanalytical techniques (e.g. cyclic voltammetry, electrochemical impedance spectroscopy). Our work is multi-disciplinary in nature, incorporating aspects of materials, analytical, synthetic, and physical chemistry.
Awards
- John Dewey Teaching Award
- Invidiual Award for Outstanding Contributions to Undergraduate Education
- Robert Kuczkowski Endowed Faculty Research Award
- Camille Dreyfus Teacher-Scholar Award, 2013
- Alfred P. Sloan Research Fellow, 2013
- Society of Electroanalytical Chemistry Young Investigator Award, 2013
- NSF Career Award, 2010
- Moore Foundation Postdoctoral Fellowship, 2007, 2008
- Ford Foundation Postdoctoral Fellowship, 2006, 2007
- National Science Foundation Graduate Student Fellowship, 2001, 2003
- Beckman Scholar Fellowship, 2000, 2001
Representative Publications
Hazelnis, J.P. and Maldonado, S.* " Electrosynthesis of Quasi-Epitaxial Crystals on Liquid Metals " J. Am. Chem. Soc., 2023, 145(50), 27616-27625
Vasquez, R.; Waelder, J.; Liu, Y.; Bartels, H.; and Maldonado, S.* " A Gauss's Law Analysis of Redox Active Adsorbates on Semiconductor Electrodes: The Charging and Faradaic Currents are Not Independent " Proc. Nat. Acad. Sci., 2022, 119(36), ee2202395119
DeMuth, J.; Fahrenkrug, E.; Ma, L.; Shodiya, T.; Deitz, J. I.; Grassman, T. J.; and Maldonado, S. "Electrochemical Liquid Phase Epitaxy (ec-LPE): A New Methodology for the Synthesis of Crystalline Group IV Semiconductor Epifilms" J. Am. Chem. Soc., 2017, 139, 6960–6968
Fahrenkrug, E.; Alsem, D. H.; Salmon, N.; and Maldonado, S. "Electrochemical Measurements in In Situ TEM Experiments" J. Electrochem. Soc., 2017, 164, 4, H358-H364
Research Areas(s)
- Analytical Chemistry
Energy Science
Inorganic Chemistry
Materials Chemistry
Sensor Science
Surface Chemistry
Sustainable Chemistry
Electrochemistry
Semiconductor Photoelectrochemistry