Transcript licini andrew sol 2014 sm

Reversible
Electrochemical Mirror
(REM) Systems
A P r o m i s i n g n e w Te c h n o l o g y f o r
Reducing Energy Consumption
Andrew Licini, under the guidance of Zachary Detweiler,
Matt Vallon and Dr. Steven Bernasek
The Bernasek Research Group
(Department of Chemistry)
Specialization: Surface Chemistry and Structure, Heterogeneous Reactions
Introduction to Reversible Electrochemical
Mirrors (REMs) and Ionic Liquids
•
Windows are important sources of
natural light but also greatly
compromise the integrity of heating
and cooling systems.
•
Reversible electrochemical mirrors
(REMs) offer a promising alternative
to these systems by reversibly
depositing metal onto clear
substrates to reflect radiant thermal
energy
•
Most REM systems currently under
research use high-boiling organic
solvents1 that preclude space
applications and present possible
environmental hazards.
•The Bernasek Group aims to address
this problem by replacing such
conventional electrolytes with ionic
liquids: organic salts that are liquid at
room temperature and yet possess
exceedingly low vapor pressures.
1.) Source: Araki, S., Nakamura, K., Kobayashi, K. et. al. Electrochemical Optical-Modulation Device with Reversible
Transformation between Transparent, Mirror, and Black. Advanced Optical Materials 24 (2012), OP122-OP126.
Layout of a Reversible Electrochemical Mirror (REM)
Indium Tin Oxide (ITO)-Coated Glass
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+
Apply Potential
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Light
Light
M
M
M
M
M
M
M
M
M+
M+
M+
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Apply Potential
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Previous Results: Optical Reflectivity
•
Originally planned to study
the optical reflectivity of our
REM system, but study was
halted when preliminary
study created poor results.
•
Maximum reflectivity only
50% vs. industrial-grade
mirror.
•
Black residue on surface,
can’t be removed with
potential.
Electrochemical Study: Silver Deposition Kinetics
10-Cycle Cyclic Voltammetry of BMIM TFSI
Cell - Silver Deposition onto ITO pane
1.20E-03
1.00E-03
Cycle #
8.00E-04
1
Current (A)
6.00E-04
2
3
4.00E-04
4
5
2.00E-04
6
-1.5
-1
0.00E+00
-0.5
0
Stripping current
(positive potential)
drops rapidly—less
silver is removed
each time, resulting
in an accumulation
on the surface.
0.5
-2.00E-04
1
1.5
7
8
9
-4.00E-04
10
-6.00E-04
Voltage (V)
Overpotential—silver has to
overcome barrier to deposit
CONCLUSION:
The first time the silver
deposits, it creates a seed
layer of silver, which more
silver deposits onto
preferentially over the ITO
surface. Surface
modification with stable
metal atoms like platinum
might allow surface to
apply more uniformly and
remove more reversibly.
SEM Imaging Study: Silver Deposition Kinetics
To right: a secondary
electron microscope (SEM)
image of silver-deposited
ITO slide
• Dendritic growth rather
than smooth surface.
• Confirmation of
voltammetry results.
• Good news: surface
can be altered to alter
deposition pattern.
Improvement of Ionic Liquid Optical Purity
BMIM TFSI
prepared without
dichloromethane
(DCM) treatments
“Ultra-Pure”-grade
BMIM TFSI from
manufacturer used
as “blank”
BMIM TFSI
prepared with
DCM wash
Quantitative Purity Analysis: UV/Vis Spectroscopy
Absorptivity of BMIM TFSI Samples in the UV/Visible/Near IR
Range
Earlier ionic liquid without DCM
wash has high absorbance in
the UV/blue range, making it
appear yellow.
3
Absorbance (AU)
2.5
2
1.5
Ionic liquid prepared with new
DCM wash method has
substantially reduced
absorbance.
1
0.5
0
0
-0.5
200
400
600
800
1000
Wavelength (nm)
Without DCM Wash
With DCM Wash
1200
Future Research
• Surface modification of ITO for more even
deposition and stripping
• Coupled reaction with copper ions to aid in
reversibility of stripping.
• Identification of yellow contaminant removed with
dichloromethane with nuclear magnetic resonance
(NMR).
• Replication with IR-transparent substrates, like
aluminum oxide.
The Princeton Summer Research Experience!
Special Thanks
Many thanks are required for:
•
Dr. Steven Bernasek, (the newly) Dr. (!!!) Zachary Detweiler, and
Matthew Vallon for their advice, supervision, and support
throughout my research (as well as the entire Bernasek and
Bocarsly groups in general).
•
Our collaborators on the Reversible Electrochemical Mirror
project at Edwards Air Force Base and Kirkenland, who
provided excellent input, advice and suggestions.
•
The United States Air Force, for funding the project at large,
and, most importantly…
•
The Princeton Environmental Institute, for giving me the funds
and opportunity to participate in this amazing research
experience!