Supercapacitors based on carbide-derived carbons synthesised using HCl and Cl2 as reactants

Abstract

Micro- and mesoporous carbide-derived carbons (CDCs) were synthesised from TiC powder via a gas-phase reaction using HCl and Cl2 within the temperature range of 700–1,100 °C. Analysis of X-ray diffraction results show that TiC-CDCs consist mainly of graphitic crystallites. The first-order Raman spectra showed the graphite-like absorption peaks at ~1,577 cm−1 and the disorder-induced peaks at ~1,338 cm−1. The low-temperature N2 sorption experiments were performed, and specific surface areas up to 1,214 and 1,544 m2 g−1 were obtained for TiC-CDC (HCl) synthesised at T = 800 °C and TiC-CDC (Cl2) synthesised at T = 900 °C, respectively. For the TiC-CDC powders synthesised, a bimodal pore size distribution has been established with the first maximum in the region up to 1.5 nm and the second maximum from 2 to 4 nm. The energy-related properties of supercapacitors based on 1 M (C2H5)3CH3NBF4 in acetonitrile and TiC-CDC (Cl2) and TiC-CDC (HCl) as electrode materials were also investigated by cyclic voltammetry, impedance spectroscopy, galvanostatic charge/discharge and constant power methods. The specific energy, calculated at U = 3.0 V, are maximal for TiC-CDC (Cl2 800 °C) and TiC-CDC (HCl 900 °C), which are 43.1 and 31.1 W h kg−1, respectively. The specific power, calculated at cell potential U = 3.0 V, are maximal for TiC-CDC (Cl2 1,000 °C) and TiC-CDC (HCl 1,000 °C), which are 805.2 and 847.5 kW kg−1, respectively. The Ragone plots for CDCs prepared by using Cl2 or HCl are quite similar, and at high power loads, the TiC-CDC material synthesised using Cl2 at 900 °C, i.e. the material with optimal pore structure, delivers the highest power at constant energy.