Electrical Double-Layer Capacitor Based on Low Aqueous Electrolyte Contents in EmimTFO Ionic Liquid

Abstract

A study has been conducted on the electrochemical properties of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EmimTFO) protic ionic liquid enhanced by adding potassium nitrate (2.5 M) aqueous solution. The properties of EmimTFO as well as mixtures diluted by molar fractions of 0.6, 0.7, 0.8, and 0.9 of KNO3 were also investigated through measurements of viscosity, density, and conductivity. In a three-electrode test run at 0.25 A g-1, the addition of 2.5 M KNO3 solution generated peak specific capacities of ~40.2 and ~85.8 mAh g-1 on the positive and negative potentials, respectively. These performances surpassed the specific capacities obtained for EmimTFO in a three-electrode run at 0.25 A g-1 using the same electrode material (activated carbon). The top-performing electrolyte mixture ([EmimTFO]0.8[2.5 M KNO3]0.2) was then used to assemble a symmetric supercapacitor, which could run at a voltage of ~2.1 V. The device was able to retain 71.35% of its capacitance after 10,000 cycles of charge and discharge. It also displayed higher specific energy and power of 22.21 Wh kg-1 and 520 W kg-1, respectively, at 0.5 A g-1 as compared to specific energies of 4.73 Wh kg-1 and 11.2 Wh kg-1 for the devices assembled with single EmimTFO and 2.5 M KNO3 as the electrolytes, respectively.