Freestanding, flexible, ultrahigh-surface area carbon nanofibers by supersonic solution blowing: Promising electrodes for supercapacitors

Abstract

Carbon nanofibers are of great technological interest, yet their large-scale production is still a challenge. For the first time, carbon nanofibers are obtained by supersonic solution blowing (SSB). Here, we produced freestanding, porous, flexible, ultrahigh-surface area carbon nanofiber webs in a single-step carbonization process of polyacrylonitrile (PAN) nanofibers. Specimens were additionally modified using phenolic resin, and furfuryl alcohol (FFA). The latter was intended to increase roughness and thus, gain surface area. It was found, however, that the modifications increased average diameter and reduced both surface area and pore volume, compared to the carbonized PAN nanofibers without surface modification. An additional modification, a specimen of composite nanofibers with embedded carbon black nanoparticles, was obtained with a fiber diameter of 60 nm and a surprising ultrahigh-surface area of 4026 m2/g. The surface-modified specimen, in which PAN nanofibers were dipped in furfuryl alcohol, revealed carbonized fibers with a diameter of 140 nm and a surface area of 1560 m²/g. When used as electrodes in symmetrical cells (coin cells), supercapacitance values in the 117 - 242 F/g range in aqueous electrolyte were measured, being comparable to those of commercial devices. The assembled symmetrical device based on specimen PAN-CB delivered high energy density and power output (27.2 Wh kg–1 at 0.77 kW kg–1 and 13.6 Wh kg–1 at 192.6 kW kg–1). Thus, the SSB technique can be used to obtain ultrahigh-surface area carbon nanofibers (> 4000 m2/g) as novel functional materials for freestanding energy storage devices without physical or chemical activation of the fibers being needed to achieve microporous structure. A fundamental fibrillary electrode area-diameter coefficient FEADC [measured in m2/(g nm)] is introduced to characterize the dependence of the specific capacitance of supercapacitor electrodes on carbon nanofiber characteristics.