High surface area carbon nanofibers derived from electrospun PIM-1 for energy storage applications

Abstract

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.