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faculty
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Stephen Maldonado
Assistant Professor of Chemistry
Ph.D., University of Texas, Austin
Electrochemistry,
Semiconductor Photoelectrochemistry, Materials Chemistry,
Surface Science, Corrosion, Heterogeneous Electrocatalysis
Phone: (734) 647-4750
E-mail: smald@umich.edu
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Maldonado Research Group |
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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.
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AWARDS
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Moore Foundation Postdoctoral Fellowship (Summer
2007 - Summer 2008)
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Ford Foundation Postdoctoral
Fellowship (Summer 2006 - Summer 2007)
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National
Science Foundation Graduate Student Fellowship (Fall
2001- Spring 2003)
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Beckman Scholar Fellowship
(Summer 2000 - Summer 2001)
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REPRESENTATIVE PUBLICATIONS
- Maldonado,
S., Knapp, D., Lewis, N. S. "Near-Ideal
Photodiodes from Sintered Gold Nanoparticle
Films and Chemically Modified Silicon" J.
Am. Chem. Soc., 2008, 130,
3300-3301
- Maldonado,
S., Plass, K. E., Knapp, D., Lewis,
N. S.; "Electrical
Properties of Junctions Between Hg
and Si(111) Surfaces Functionalized with Short
Chain Alkyls" J. Phys. Chem.
C , 200, 48,
17690-17699
- Maldonado, S., Smith,
T., Williams, R., Morin, S., Barton, E.,
Stevenson, K. J., "Surface
Modification of Indium Tin Oxide
via Electrochemical Reduction of
Aryldiazonium Cations" Langmuir, 2006,
22, 2884-2891
- Maldonado, S., Stevenson,
K. J., "Influence
of Nitrogen Doping on Oxygen Electrocatalysis
at Carbon Nanofiber Electrodes" J.
Phys. Chem. B, 2005,
109, 4707-4716
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