Less Water, Naked Choline, and Solid Iodine for Superior Ecofriendly Hybrid Energy Storage

Abstract

Hybrid supercapacitors are a variant of electrochemical capacitors that can store and deliver high specific energy without significantly compromising on power performance. A hybrid supercapacitor takes the advantage of hybridizing a supercapacitor electrode with a battery-like electrode. [1][2][3][4][5][6] A prime example is a lithium-ion capacitor that uses a graphite intercalation-based battery electrode and a supercapacitor electrode made from activated carbon in an organic electrolyte. [7,8] An ecofriendly and low-cost alternative is a hybrid supercapacitor with redox moieties (e.g., iodides) dissolved in an aqueous electrolyte. [9][10][11] Iodide-based aqueous electrolytes form a sustainable system for hybrid supercapacitors due to the highly reversible iodide/ iodine redox couple (E 0 ¼ þ0.54 V versus standard hydrogen electrode, SHE) at the positive electrode or cathode, whereas the negative carbon electrode stores the charge physically in the electric double-layer (EDL).Due to the high mobility of ionic species resulting in high ionic conductivity, aqueous electrolytes are adapted for high power performance of supercapacitors. [12] In this regard, iodide salts dissolved in aqueous supporting electrolyte achieve a high voltage window and capacity. The presence of a supporting electrolyte provides high over-potential for di-hydrogen evolution at the negative carbon electrode and simultaneously limits polyiodide shuttling. [9] Nevertheless, the high

A unique choline nitrate-based organo-aqueous electrolyte enables carbon/carbon supercapacitor operation in a wide temperature window (−40°C to 60°C)

“…Choline nitrate (ChNO 3 ) was produced from choline chloride (ChCl) through a metathesis reaction by exchanging chloride with nitrate, according to the procedure described in the literature ( Curnow et al, 2018 ; Abbas et al, 2021 ). The electrolyte solution was prepared with a concentration of 5 mol/kg by dissolving the weighed amount of salt in distilled water.…”