Electrical Double Layer Capacitors Based on Steam and CO2-Steam Co-Activated Carbon Electrodes and Ionic Liquid Electrolyte

Abstract

EDLCs based on micro-mesoporous carbon electrodes prepared from steam and CO2-steam co-activated SiC-CDCs and room-temperature ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate as an electrolyte were tested to establish the electrochemical power and energy densities and region of ideal polarizability. Cyclic voltammetry, constant current charge/discharge (CC/CD), electrochemical impedance spectroscopy (EIS) and constant power discharging methods have been applied to establish the electrochemical characteristics of EDLCs completed. The highest capacitance value of 162 F g−1 at 3.6 V has been established by EIS for the SiC-CDC material, which was activated with steam at 1000°C and cleaned with molecular H2. The capacitance values for other materials prepared using the steam activation process at different temperatures were only slightly lower. The calculated coulombic efficiency values from constant current discharge/charge data for all the systems remained within the range from 97.0 to 98.5% and from 99.3 to 100% at current densities 0.1 A g−1 and 1 A g−1, respectively. The coulombic efficiencies calculated from integrated cyclic voltammetry plots varied from 97 to 98 and from 99 to 100% at potential scan rates 5 and 50 mV s−1, respectively, showing that the steam activated SiC-CDC materials are very promising for various high energy density storage/generation applications.