Pore-Engineered Ultrahigh Surface Area Okra-Derived Activated Carbon for Concurrently High-Power-Density and High-Energy-Density Supercapacitor

Simultaneously, high energy and power density are extremely desirable attributes in supercapacitors. Carbon-based supercapacitors deliver high power but cannot retain significant energy density at high charging rates. Herein, it is demonstrated that the prudent selection of okra as a carbon precursor, diligent processing, and use of water-in-salt electrolyte (WiSE) to expand the voltage window ensures both high energy and high-power density. Okra is an ideal carbon precursor as it contains a significant amount of water and minerals. Their methodical removal during processing yields okra-derived activated carbon (OAC), having an ultrahigh surface area of 2109 m2 g-1 with an effective combination of micro/meso/macropores. The electrochemical studies of OAC in a three-electrode system using 6 m KOH as an electrolyte display an outstanding capacitance of 318 F g-1 at 1 A g-1. Furthermore, the potential window is extended to 1.6 V using a WiSE (27 molal CH3COOK). This leads to a remarkable increase in energy density to 44.44 Wh kg-1 with an extraordinary power density of 80,000 W kg-1 at 50 A g-1 in two-electrode system. 100% capacitance retention is observed after 10,000 cycles at 10 A g-1. This study highlights the importance of pore engineering for superior electrochemical performance.