Electrochemical Zinc Ion Capacitors Enhanced by Redox Reactions of Porous Carbon Cathodes

Aqueous electrochemical zinc ion capacitors (ZICs) are promising next-generation energy storage devices because of their high safety, inexpensive raw materials, and long cycle life. Herein, an aqueous ZIC with superior performance is fabricated by employing an oxygen-rich porous carbon cathode. Excellent capacitance and energy density are obtained thanks to the electric double-layer capacitance of porous carbon, and additional pseudocapacitances originating from the variation in oxidation states of oxygen functional groups and the reversible electrochemical hydrogen adsorption and desorption during each round-trip charge–discharge cycle. Moreover, the cycling stability of ZIC is effectively prolonged by suppressing zinc dendrite growth with a simple surface carbon coating strategy. The assembled ZIC delivers a high capacitance of 340.7 F g−1, a high capacity of 179.8 mAh g−1 in a wide voltage window of 0–1.9 V, a maximum energy density of 104.8 Wh kg−1, and an ultrahigh power density of 48.8 kW kg−1. Furthermore, the as-fabricated aqueous ZIC exhibits an ultralong cycle life of 30 000 cycles with a high capacity retention of 99.2%. This work provides a novel design strategy by incorporating reversible hydrogen and oxygen redox reactions to enhance the energy storage capability of aqueous ZICs toward practical energy storage applications.