Electric Double Layer Capacitance of Activated Carbon Nanofibers in Ionic Liquid: EMImBF4

Abstract

The double layer capacitance of an activated carbon nanofiber (ACNF) with a 100∼200 nm fiber-diameter, prepared by the polymer blend spinning technique, was investigated using 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4) as the electrolyte. The conventional activated carbon fiber (ACF) with the fiber-diameter of ∼10 µm and narrow micropores (∼0.7 nm pore-width) showed a significant irreversible adsorption of EMIm+ cation in EMImBF4, however, the ACNF effectively suppress the irreversibility even with the pore structure comparable to the conventional ACF. This suggests the effect of the short pass length on the ion adsorbing/desorbing process. The decreased capacitance by the cycling in EMImBF4 was recovered by the addition of propylene carbonate as an organic solvent to the electrolyte. This means that the irreversible adsorbed ions can be desorbed using propylene carbonate.