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.