Introduction

1. Summer Research Project: ELECTROCHEMICAL CAPACITORS C.S.Peterson; M.P.Yeager; W.Du; X.Teng The Joan and James Leitzel Center for Science, Technology, Engineering and Math Education: Research Experience for Teachers in Engineering Program 2012 EEC-1132648 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 A change in particle size was noted through settling (Stokes’ Law) in 50/50 % in-situ polymerizered pyrrole /Mn3O4, providing evidence of reaction. Larger particle size was even more apparent in the 90/10 % in-situ polymerizered pyrrole / Mn3O4, both in comparison to metal oxide alone. To facilitate charge transfer of the Faradaic reaction of : Mn3+ Mn4+ + e- a conductive polymer, polypyrrole, (PPy), was formed from the monomer in-situ with nanoparticle metal oxide. 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. 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. Introduction 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. 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 Conclusions • Electrochemical capacitors, double layer (EDLC) and psuedo-capacitors (redox), differ from static capacitors as they use electrolytes. • Emerging energy applications for ECs with characteristics of high power and improved energy densities has prompted research into materials for electrodes. TEM images were taken from samples suspended in ethanol, prepared and dried on Formvar/Carbon copper wire mesh. TEM images are at 40,000 x magnification. Clear evidence of polymer surrounding metal oxide nanoparticles. • TEM photographs verified conductive polypyrrole surrounding Mn3O4 metal oxide nanoparticles. Pyrrole monomer was transformed in-situ. • Reducing the distance for electron transfer in the Faradaic reaction between the electrolyte, metal oxide and electrode may enhance performance in psuedo-capacitors. • In-situ polymerization of conductive polymer allows contact at the nanometer scale to the metal oxide. • The optimization of electrode materials are critical for further development. Increasing the surface area through synthesis of nanometer size particles increases surface reactions. • 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. * Kotz et al. (2000) 50/50 % by wt PPy/Mn3O4 • 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. • 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. • 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 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 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. 90/10 % by wt PPy/Mn3O4 Further Investigations • 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. Synthesis: Nanoparticle Metal Oxide Mn3O4 Half Cell Results  Compared cyclic voltammogram specific capacitance 100 % Mn3O4 (+ 20% PTFE non-conductive) 50/50 % in-situ polymerizeredpyrrole / Mn3O4 90/10 % in-situ polymerizeredpyrrole / Mn3O4 100 % polymerizeredpyrrole Acknowledgements • UNH Department of Chemical Engineering, Dr. XaioweiTeng. • 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. 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: Specific Capacitance at 100th cycle: 100 % Mn3O4(+ 20% PTFE) 70.3 F/g 50/50 % PPy/Mn3O4 109.1 F/g 90/10 % PPy/Mn3O4 2.0 F/g 100 % PPy 0.8 F/g Cyclic Voltammogram, 50 mV/s scan rate Mn3O4, metal oxide only References 7/12/12 synthesis Mass on electrode of 5 micrograms total; therefore Mn3O4 loading was reduced while PPy was increased. • 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) Prepared dilute solution MnCl2 10 mL of H2O 70mg MnCl2*4H2O 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 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. 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. Three electrode apparatus