Effect of carbon nanofibers on electrode performance of symmetric supercapcitors with composite α-MnO2 nanorods

Abstract

α-MnO2 nanorods have been grown on the surface of carbon nanofibers (CNFs) for enhancing the electrical conductivity of MnO2. We have synthesized α-MnO2/CNF (0–5 wt%) nanocomposites using a co-precipitation method. The x-ray diffraction results confirm the formation of a single phase α-MnO2 and SEM/TEM images reveal the formation of α-MnO2 nanorods, whose size depends on the amount of CNF in the nanocomposite. Both the surface area and electrical conductivity of nanocomposites are found to be strongly influenced by the presence of CNF. While α-MnO2/CNF(1.25 wt%) exhibits the largest surface area (381 m2/g) and only a modest increase in the electrical conductivity compared to pure α-MnO2 nanorods, the α-MnO2/CNF(5 wt%) shows the least surface area (131 m2/g) but an order of magnitude higher electrical conductivity (0.67 S/cm). Cyclic voltammetry measurements show improved performance (higher specific capacitance and better cyclic stability) in all α-MnO2/CNF supercapacitors compared to that of pure α-MnO2. Ragone plot shows that although α-MnO2/CNF(1.25 wt%) exhibits the highest specific capacitance (313 F/g at 1 A/g) and hence the highest energy density of 32.8 Wh/kg, it has the least power density of 4250 W/kg. On the other hand, α-MnO2/CNF(5 wt%) shows the least energy density of 7.9 Wh/kg but with a higher power density of 8478 W/kg compared to α-MnO2/CNF(1.25 wt%). Our studies demonstrate that one can optimize both energy and power densities by controlling the amount of CNF in the nanocomposites.