Stable ionic-liquid-based symmetric supercapacitors from Capsicum seed-porous carbons

In this study, a symmetric ionic-liquid based supercapacitor was assembled with porous carbon derived from Capsicum (bell pepper) seeds. The “peppered”-activated carbon (ppAC) was synthesized using varying amounts of KHCO 3 activating agent (AA) at 850 \ub0C carbonization temperature. The best device performance reported was recorded with optimum amounts of AA to raw material. The need for less amount of AA is crucial if the entire activation/carbonization process is to be scaled-up with the cost and final product yield also being important for a viable synthesis. A mechanism of saturation of pores with unreacted AA which leads to lower porosity metrics in the samples with increasing the amount of AA during carbonization/activation was also proposed. Using an ionic liquid electrolyte, 1-ethyl-3-methylimidazolium bistrifluorosulfonylimide (EMIM-TFSI), the ppAC-based supercapacitor operated up to a maximum cell voltage of 3.20 V. A specific energy of 37 Wh kg −1 was obtainable with a corresponding practical power density of 0.6 kW kg −1 at 0.5 A g −1 . A specific energy of ∼26 Wh kg −1 was still achievable when the applied current was doubled to 1.0 A g −1 and a high cyclic stability (approx. 99% coulombic efficiency) was proven over 25,000 cycles. Further ageing test performed on the device revealed a remarkable improvement in the electrochemical performance after a 180 h (ca. 1 week) floating time. The obtained results also confirmed a uniquely distributed porous carbon in which the complete utilization of the entire less-corrosive KHCO 3 AA for optimal pore activation at elevated carbonization temperatures. Thus, the efficient design combinations for stable, high-energy and power ionic liquid-based supercapacitors with cheaper biomass-based materials are demonstrated