Narrow-porous pitch-based carbon fibers of superior capacitance properties in aqueous electrolytes

Abstract

Two couples of narrow-porous carbons in the form of particulates (PAC) and fibers (ACF) have been prepared by one step carbonization/activation of pitch-based precursors in carbon dioxide or ammonia atmosphere. The activated carbons are assessed as electrode material of EDL capacitor operating in 6molL−1 KOH and 0.5molL−1K2SO4 aqueous solutions. Electrochemical measurements show distinctly improved charge propagation in pitch-based ACFs compared to corresponding PACs but also to commercial phenolic resin-based FR15 fibers of very similar porosity characteristics, especially in the sulphate medium. Over twice higher capacitance of ACFs than FR15 in K2SO4 solution (over 90 vs 40Fg−1 at 1Fg−1) is attributed to less distorted basic structural units in pitch-based fibers, and thus facilitating quick penetration of ions along pores. Carbonization/activation treatment in ammonia appears to be a very effective route for enhancing the capacitance without noticeable negative impact of nitrogen and oxygen functionalities with increasing charge rate, current density or frequency. Pitch-based narrow-porous active carbon fibers seem to be a very well adapted candidate for use as electrode material of low-to-moderate power capacitor intended to operate in sulphate electrolyte above water decomposition voltage.