Deep eutectic solvents as effective electrolyte from potassium iodide and ethylene glycol exhibiting redox behavior for supercapacitor application

In present work, an efficient deep eutectic solvents (DESs) system based on KI and ethylene glycol (EG) has been successfully constructed and used as an electrolyte for supercapacitors in wide temperature range. The DESs electrolytes represent good electrochemical performance and the maximum specific capacitance reaches 217 F g−1 and the energy density is 18.42 Wh kg−1 at 0.7 kW kg−1. It is noteworthy that the DESs electrolytes can produce pseudocapacitance. Consequently, the total pseudocapacitance of supercapacitors is contributed by the redox reaction of KI as well as the redox reaction of oxygen-containing functional groups on the surface of activated carbon. Meanwhile, iodine-related ions and unbonded hydroxyl group of DESs electrolytes form hydrogen bonds with the oxygen-containing functional groups, accelerating the migration of electrolytes ions. Additionally, it is found that the internal composition of DESs electrolytes plays a vital effect on its properties. Resultantly, DESs with a molar ratio of KI to EG of 1:7 delivers the highest conductivity (1.22 mS cm−1) and the lowest viscosity (39.77 cP), exhibiting best electrochemical performance. The present novel DESs electrolyte paves the way for application of non-aqueous redox additives in supercapacitors, simultaneously delivering hydrogen bonding between solvent and redox additive.