Carbon Nanocoils as Unusual Electrode Materials for Supercapacitors

Abstract

Carbon nanocoils (CNCs) are coiled carbon nanofibers of ca. 10 nm in fiber diameter, and 10–20 nm in internal coil diameter. They are prepared through several oxidation treatments, which lead to a graduate content in surface oxygen groups evolving as either CO or CO2 in temperature-programmed desorption. The CNCs show a moderate surface area (40–240 m2 g−1) and a relatively high electrical conductivity (0.1–0.2 S cm−1). Some CNCs are activated to develop surface area. The electrochemical behaviour of CNCs as supercapacitor electrode is studied in the electrolytes H2SO4 and Et4NBF4. From the parameters C1 (overall specific capacitance measured at 1 mA cm−2), SBET (BET specific surface area), and CO and CO2 content, the plots of C1/SBET vs. CO/SBET and vs. CO2/SBET are analyzed. In the acidic electrolyte, the oxygen groups evolving as CO2 contribute significantly to enhance C1 in addition to the groups evolving as CO. C1/SBET shows a linear dependence, with high slope, on CO2/SBET, and an exponential dependence on CO/SBET. In the organic electrolyte, the two kinds of oxygen groups contribute less to C1. The specific pseudocapacitance and double layer capacitance are determined and discussed in relation to the CO and CO2 content and the SBET value.