Flexible supercapacitors based on low-cost tape casting of high dense carbon nanofibers

This experimental study, reports the use of flexible tape casting of dense carbon nanofiber (CNFs) alone and in hybrid structure with MnO2 for supercapacitor applications. Different electrolyte concentrations of potassium hydroxide (KOH) were tested and it was founded that mild concentrated electrolyte, like 9 M KOH, provides higher specific capacitance 38 F g−1 at a scan rate of 5 mV s−1. Electrochemical impedance spectroscopy (EIS) measurements explain that the solution resistance and the charge transfer resistance is higher for 3 M KOH concentrations and lower for 6 M KOH concentrations. Afterwards a novel, fast and simple method is adopted to achieve a hybrid nanostructure of CNFs/MnO2 with various KMnO4 ratios. The hybrid supercapacitor, having loaded a mass of 0.0003 g MnO2 as a thin film, delivers a highest specific capacitance of 812 F g−1 at a scan rate 5 mV s−1. Charge/discharge cycling stability at current density of 7.9 A g−1 demonstrates larger specific capacitance 303 F g−1 and stability. Furthermore, the hybrid supercapacitor can deliver specific energy (72.4 Wh kg−1) at specific power (3.44 kW kg−1). Specific surface area increase from 68 m2 g−1 for CNFs to 240 m2 g−1 for CNFs/MnO2.