A Chlorine-Based Redox Electrochemical Capacitor.

Electrochemical capacitors are under the spotlight due to their high power density, but they have a low energy density. Redox electrolytes have emerged as a promising approach to design high-energy electrochemical energy storage devices. Herein, a chlorine-based redox electrochemical capacitor is reported in an ionic liquid electrolyte. The commercial activated carbon is employed as the working electrode to render the reversible redox of chloride ions in an ionic liquid, by the restriction of micropores on neutral chlorine. The carbon material can simultaneously provide electrical double-layer capacitance. The effective integration of a chlorine redox reaction and electrical double layer allows for high-energy electrochemical capacitors. By this means, a rechargeable chlorine-based redox electrochemical capacitor with reversible capacity and good rate capability and cycling stability is obtained. This work offers a solution for a new type of high-energy electrochemical capacitors.