Browsing by Author "Bonso, Jeliza S."
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Item High Surface Area Carbon Nanofibers Derived from Electrospun Pim-1 for Energy Storage Applications(2013-11-21) Bonso, Jeliza S.; Kalaw, Grace Jones D.; Ferraris, John P.; Bonso, Jeliza S.; Kalaw, Grace Jones D.; Ferraris, John P.Electrochemical double layer capacitors (EDLCs) utilize electrodes with high surface area to achieve high-energy storage capability. In this study, flexible and freestanding carbon nanofibers derived from PIM-1, a microporous polymer with high free volume, were prepared by pyrolysis of the electrospun polymer. A BET surface area of 546 m² g⁻¹ was obtained upon carbonization of the electrospun PIM-1 fibers. After further heat treatments such as steam-activation and annealing, the surface area increased to 1162 m² g⁻¹. These carbon fibers were directly used as electrodes without the use of binders in a coin cell (CR2032) configuration and were characterized by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy. The activated and annealed fibers gave a specific capacitance of 120 F g⁻¹ at a scan rate of 10 mV s⁻¹ using 1,3-ethylmethylimidizaolium bis(trifluoromethanesulfonyl) imide as the ionic liquid electrolyte. From the galvanostatic charge-discharge test, the supercapacitor exhibited energy and power densities of 60 W h kg ⁻¹ (active material) and 1.7 kW kg⁻¹, respectively, at a current density of 1 A g⁻¹. High power application of this device was demonstrated by its 77% retention of the energy density (47 W h kg⁻¹) at a higher discharge current density of 5 A g⁻¹.Item Optimization of polybenzimidazole-based nanofibers for supercapacitor electrode applications(2013-05-21) Charlton, John; Bonso, Jeliza S.; Ferraris, John P.; The University of Texas at Dallas. Office of Undergraduate Education.; The University of Texas at Dallas. Office of Research.Electrochemical capacitors (supercapacitors) are energy storage devices characterized by high energy and power densities with long cycle stability. Supercapacitor research focuses on improving the device's energy density to be more competitive with existing battery technology. Because of their large power. densities, supercapacitors may find application anywhere a quick charge of electricity is needed, like regenerative braking systems or consumer electronics. Supercapacitors store energy in the electrochemical double-layer. When a substrate is charged in an electrolytic solution, the substrate will attract the oppositely charged electrolyte ion. This interaction forms a double-layer and is the mechanism of charge storage for supercapacitors. Since charge storage depends on this electrode/electrolyte interface, the electricity a supercapacitor can store is directly proportional to its available surface area. In this work, carbon nanofibers from the precursor polymer polybenzimidazole (PBI) were produced through electrospinning to achieve high surface area electrodes. After the fibers are produced, they undergo a series of treatments to improve their surface area. In addition, ammonium bicarbonate is used as a sacrificial pore-generating agent (porogen) to produce cavities capable of accommodating more ions. Energy is related to capacitance through the equation E = ½ CV², so energy storage can be improved with a higher working voltage. The ionic liquid ethylmethylimidazolium bis(trifluoromethylsulfonyl)imide was chosen as the electrolytic solution with a working voltage of 4.1V.