Optimization of polybenzimidazole-based nanofibers for supercapacitor electrode applications

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.