Stephen Maldonado

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 gallium phosphide (an inorganic semiconductor) surfaces with various organic functional groups and to use linking chemistries to attach electrocatalytic materials to these surfaces. Another area of exploration is the development, study, and application of unexplored classes of semiconductor materials such as transition metal nitrides and oxynitrides. 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
• Society of Electroanalytical Chemistry Young Investigator Award, 2013
• NSF Career Award, 2010

Representative Publications

Acharya, S.; Lancaster, M.; Maldonado, S. "Semiconductor Ultramicroelectrodes: Platforms for Studying Charge-Transfer Processes at Semiconductor/Liquid Interfaces" Anal. Chem., 2018, ASAP

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

Gu, J; Collins, S. M.; Carim, A. I.; Hao, X.; Bartlett, B. M.; and Maldonado, S. "Template-Free Preparation of Crystalline Ge Nanowire Film Electrodes via an Electrochemical Liquid-Liquid-Solid Process in Water at Ambient Pressure and Temperature for Energy Storage" Nano Lett., 2012

Research Areas(s)

• Analytical Chemistry
  Energy Science
  Inorganic Chemistry
  Materials Chemistry
  Sensor Science
  Surface Chemistry
  Sustainable Chemistry
  Electrochemistry
  Semiconductor Photoelectrochemistry

Fellowships

• Alfred P. Sloan Research Fellow, 2013
• 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