Sustainable Development of Interconnected Hierarchical Porous Carbon From Rice Panicle Waste: Synergistic KOH / CO 2 Dual‐Activation Strategy for Advanced Symmetric Supercapacitors

ABSTRACT Herein, agricultural waste of rice panicles was adopted as a raw precursor to prepare PAC using KOH activation at different concentrations (0, 0.25, 0.50, and 0.75 M) coupled with CO 2 activation at 850°C and its implementation as symmetric supercapacitor electrodes. RPPAC‐0.25‐850 exhibited high S BET , hierarchical porosity, and a high degree of graphitization. At 1 A g −1 , RPPAC‐0.25‐850 attained a gravimetric capacitance of 280 F g −1 , Coulombic efficiency of 86.53%, and an impressive energy density of 38.95 Wh kg −1 at a power density of 413.5 W kg −1 . Likewise, the RPPAC‐0.25‐850‐based symmetric SC device exhibited high GCD cycling stability, retaining 88% capacitance at 10 A g −1 after 6000 GCD cycles, suggesting superior capacitance efficiency. The results suggest that agricultural waste can be a sustainable energy storage solution, with optimal KOH activation conditions for exceptional SC performance, and also offers a viable potential route for greener, more efficient energy solutions.