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.
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
Chitambar, M. J.;* Wang, Z.;* Liu, Y.; Rockett, A.; Maldonado, S. "Dye-Sensitized Photocathodes: Efficient Light-Stimulated Hole Injection into p-GaP Under Depletion Conditions" J. Am. Chem. Soc., 2012, 134, 10670-10681
Peczonczyk, S. L.; Mukherjee, J.; Carim, A. I.; Maldonado, S. "Wet Chemical Functionalization of III-V Semiconductor Surfaces: Alkylation of Gallium Arsenide and Gallium Nitride by a Grignard Reaction Sequence " Langmuir, 2012, 28, 4672-4682
Hagedorn, K.; Forgacs, C.; Collins, S. M.; and Maldonado, S. "Design Considerations for Nanowire Heterojunctions in Solar Energy Conversion/Storage Applications" J. Phys. Chem. C, 2010, 114, 12010-12017