A novel hierarchical porous activated carbon-organic composite cathode material for high performance aqueous zinc-ion hybrid supercapacitors

Zinc-ion hybrid supercapacitors (ZIHSCs) are among the most promising electrochemical energy storage technologies because of their high energy density, environmental sustainability, low price, and inherent security. Hence, we have developed a novel energy storage system that uses a hierarchical porous activated carbon with redox-active organic materials as an active hybrid cathode material for ZIHSCs. The large surface area of chitosan-derived activated carbon (Ch-C), the fast electron transfer mechanism of bis-glycinyl naphthalene diimide (H2BNDI), and zinc's bivalent nature all together contribute to the high energy density of redox-active zinc-ion hybrid supercapacitors (RAZIHSCs). The fabricated device exhibited an outstanding energy output of 250 Wh kg−1 @ 0.1 A g−1 and a power output of 9.5 kW kg−1 @ 10 A g−1 due to the additional pseudocapacitive behaviour arising out of the redox-active H2BNDI material. Additionally, 100% coulombic efficiency and 80% capacitance retention are still attained after 10000 cycles at a high current density of 5 A g−1. As a result of the complex chemical reactions between Zn2+-ions and H2BNDI moiety in the composite cathode, the proposed RAZIHSCs demonstrated a lower self-discharge rate (23% in 25 h) with extremely low leakage current density (15 mA g−1).