Summer Research Project:
EEC-1132648
The Joan and James Leitzel Center for
Science, Technology, Engineering and Math
Education: Research Experience for
Teachers in Engineering Program 2012
ELECTROCHEMICAL CAPACITORS
C.S.Peterson; M.P.Yeager; W.Du; X.Teng
In-situ polymerization of pyrrole on metal oxide nanoparticles for pseudo-capacitors
Topic: METAL OXIDE NANOSTRUCTURES AS FARADAIC
REDOX REACTIONS FOR ENERGY STORAGE APPLICATION
OPTIONS WITH POWER AND ENERGY DENSITIES
BETWEEN BATTERIES AND CAPACITORS
Goal: Can a coating of polypyrrole on a nanoparticle metal
oxide be prepared by in-situ polymerization to improve the
specific capacitance by reducing charge-transfer resistance over
the electrode/metal oxide interface?
In-Situ Polymerization
To facilitate charge transfer of the Faradaic reaction of :
3+
4+
Mn
Mn + e
Polypyrrole, a known conductive polymer, was assembled from
the pyrrole monomer in dilute aqueous solution in order to
surround metal oxide nanoparticles.
A sample of Mn3O4 from synthesis, mass of 10.2 mg was diluted with 4.450 mL to a 0.010M aqueous solution
which was sonicated for 10 minutes prior to and 10 additional minutes after adding 105 mL of a 10% pyrrole
monomer dissolved in ethanol. To initiate polymerization 105 mL of 0.010M aqueous Fe(NO3)3 was added,
followed by 30 minutes of sonication. The sample was centrifuged and dried. Small dimension particles
appeared to settle.
Electrochemical capacitors (EC) store energy in an electric field that can
be charged and discharged rapidly. These electrochemical capacitors are
useful in combination with conventional batteries by providing electrical
energy storage and release where rapid high power delivery or uptake is
needed. Though small, single cell, low voltage EC have been commercially
available, different applications require improved energy density.
* Kotz et al. (2000)
• Emerging energy applications for ECs with
characteristics of high power and improved
energy densities has prompted research
into materials for electrodes.
• Psuedo-capacitors or redox-capacitors are a class of EC energy
storage devices that fill the gap between batteries with high energy
densities and electrostatic capacitors with high power densities.
• Psuedo-capacitors rely on metal oxides nanomaterials which undergo
fast and reversible surface reactions for charge storage.
A similar method was used in the preparation of the 9 to 1 sample pyrrole / Mn3O4, using 9 times the amount of
pyrrole and Fe(NO3)3. The particle size that settled was noticeably larger and descended at an increased rate.
Mn3O4, metal oxide only
• Reducing the distance for electron transfer in the Faradaic reaction
between the electrolyte, metal oxide and electrode may enhance
performance in psuedo-capacitors.
Clear evidence of polymer surrounding
metal oxide nanoparticles.
• In-situ polymerization of conductive polymer allows contact at the
nanometer scale to the metal oxide.
50/50 % by wt PPy/Mn3O4
The 15-20 nm octahedral shape Mn3O4 particles
can still be visualized, though the particles appear to be
clumped together in 100-300 nm structures. The lighter
gray, more evident in the 90/10, is assumed to be the
polypyrrole compound.
• The optimization of electrode materials are critical for further
development. Increasing the surface area through synthesis of
nanometer size particles increases surface reactions.
The true particle size of the PPy / Mn3O4 are not clear,
and may perhaps not be distinct individually coated
particles. The aggregate particle size appears to be
less than 1000 nm. More importantly, however, they
have a high surface area structure.
Half Cell Results
100 % Mn3O4 (+ 20% PTFE)
50/50 % PPy/Mn3O4
90/10 % PPy/Mn3O4
100 % PPy
90/10 % by wt PPy/Mn3O4
Further Investigations
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70.3
109.1
2.0
0.8
F/g
F/g
F/g
F/g
100 % Mn3O4 (+ 20% PTFE non-conductive)
50/50 % in-situ polymerizered pyrrole / Mn3O4
90/10 % in-situ polymerizered pyrrole / Mn3O4
100 % polymerizered pyrrole
Mass on electrode of 5 micrograms total; therefore
Mn3O4 loading was reduced while PPy was increased.
Discussion
The data graphed represents a single
synthesis and is shown at the 100th cycle.
Only a limited number of half cell tests were
completed and though results appeared
promising, they were inconsistent.
Three electrode apparatus
• Reducing the resistivity to the electron charge transfer to the electrode
from the Faradaic reaction may enhance the specific capacitance and
charge / discharge cycle endurance of the psuedo-capacitor.
Compared cyclic voltammogram specific capacitance
Specific Capacitance at 100th cycle:
Prepared 0.300 M KOH:
10 mL of H2O
163 mg KOH
Placed in Syringe Pump
Added with programmable syringe pump at rate of 0.167 mL per
minute:145 mg KOH / 8.33 mL used. Allowed 30 minutes stirring to
react. Centrifuged for 10 minutes. Decanted and consolidated and
washed with H2O and centrifuged for 10 minutes. Decanted and
washed with ethanol and centrifuged 10 minutes. Decanted and
vacuum dried at room temp for 16 hours. TEM sample prepared
on Formvar/Carbon copper wire mesh
• TEM photographs verified conductive polypyrrole surrounding Mn3O4
metal oxide nanoparticles. Pyrrole monomer was transformed in-situ.
TEM images are at 40,000 x magnification.
7/12/12 synthesis
Prepared dilute solution MnCl2
10 mL of H2O
70mg MnCl2*4H2O
Conclusions
TEM images were taken from samples
suspended in ethanol, prepared and dried on
Formvar/Carbon copper wire mesh.
• This is an investigation to enhance the conductivity of the redox
material by reducing the distance electrons travel between the metal
oxide and the electrode by creating a nanometer thickness layer of a
conductive polymer on the metal oxide through in-situ polymerization.
The metal oxide, Mn3O4, was characterized
for psuedo-capacitor use per a synthesis
method devised by Matt P. Yeager. The
particle size verification, done by TEM, of
15-20 nm, is shown below:
The above TEM photo to the right highlights the conductive polymer in green
and attempts to identify some octahedral shaped Mn3O4 particle edges in purple.
TEM Results
• Materials should be low cost, have multiple oxidation states, large
specific capacitance and long life cycling based on their potential for
electron transfer during Faradaic reactions.
Synthesis: Nanoparticle Metal Oxide Mn3O4
Larger particle size was even more apparent in the
90/10 % in-situ polymerizered pyrrole / Mn3O4, both
in comparison to metal oxide alone.
a conductive polymer, polypyrrole, (PPy), was formed from the
monomer in-situ with nanoparticle metal oxide.
Introduction
• Electrochemical capacitors, double layer
(EDLC) and psuedo-capacitors (redox),
differ from static capacitors as they use
electrolytes.
A change in particle size was noted through settling
(Stokes’ Law) in 50/50 % in-situ polymerizered
pyrrole /Mn3O4, providing evidence of reaction.
Cyclic Voltammogram,
Comparison to other ratios of PPy/Mn3O4 for optimization or other conductive polymers.
Comparison to commercial manufactured polymer. Amalgamated versus in situ.
Centrifuge methods to reduce opaque supernatant on 2nd wash.
Improve precision with multiple synthesis and more measurable quantities.
Cycle charge / discharge testing of full (button) cells.
Acknowledgements
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UNH Department of Chemical Engineering, Dr. Xaiowei Teng.
Matthew P. Yeager and Wenxin Du for encouraging me to be independent, allowing me to pursue a distinct research project,
utilizing and competing for their resources, and for being patient when enduring and answering my unending questions.
Matthew Sullivan and Dom Montollo for coaching with laboratory synthesis and testing procedures.
Carole Lessard, Katie Stella, Baron Richardson, Michelle Kelly, Berkley Sadana and April Cartwright for their camaraderie,
inspiration, and sharing of their instructional experiences in a professional development manner.
Nancy Cherim, at UNH-UIC for access, training and assistance in TEM photography.
Brad Kinsey, NSF Grant recipient, and Stephen R. Hale, at the Leitzel Center, for coordinating the RETE program and providing
defined direction, appropriate resources, confident leadership and encouragement throughout this experience.
50 mV/s scan rate
References
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Chen, Li-Li; Wu, Xing-Long; Guo, Yu-Guo; Kong, Qing-Shan; Xia, Yan-Zhi, “Synthesis of Nanostructured Fibers Consisting
of Carbon Coated Mn3O4 Nanoparticles and Their Application in Electrochemical Capacitors Journal of Nanoscience and
Nanotechnology,, Volume 10, Number 12,, pp. 8158-8163(6) (2010)
Eftekhari, Ali, Editor; Nanostructured Conductive Polymers, Wiley; p293 Table 7.1 (2010)
Kotz, R. and Carlen, M. “Principles and Applications of Electrochemical Capacitors”, Electrochimica Acta; Volume 45, Issues
15-16, pp 2483–2498 , 3 May (2000) *Graphic used.
Park, J.E.; Atobe, M., Fuchigami, T.; “Sonochemical synthesis of conducting polymer-metal nanoparticle composite”,
Electrochimica. Acta., 51, 849-854 (2005)
Wang, Y.; Zou, B.; Gao,Y.; Wu, X.; Lou, S. and Zhou, S. “Synthesis of orange-like Fe3O4/PPy composite microspheres and
their excellent Cr(VI) ion removal properties”, J. Mater. Chem., 22, 9034-9040 (2012)
Cat Peterson is an in-service high school teacher in Naugatuck, CT. Prior to teaching, she earned a B.S. in Chemistry from the University
of Connecticut and enjoyed ten years of S.T.E.M. careers, holding jobs as application chemist, quality director, product/ project manager
and program launch leader for a variety of engineered polymer composite manufacturers. Cat then became certified in 7-12 grade
Chemistry and General Science, and teaches Academic and Honors chemistry to sophomores and juniors along with diverse science
electives. After earning her M.S. in Chemistry from Saint Joseph College in 2009, she had been reenergized in promoting S.T.E.M.
education and career awareness. This opportunity to conduct summer research in a S.T.E.M. area through the National Science
Foundation grant awarded to the James and Joan Leitzel Center at the University of New Hampshire, Durham, NH. has empowered her
to encourage, excite and teach students to appreciate science, math, technology and engineering.