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 m 2 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 CH 3 COOK). 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.