| Summary: | In this research, we successfully produced hierarchical porous activated carbon from biowaste employing one-step KOH activation and applied as ultrahigh-performance supercapacitor electrode materials. The coconut shell-derived activated carbon (CSAC) features a hierarchical porous structure in a honeycomb-like morphology, leading to a high specific surface area (2228 m<sup>2</sup> g<sup>−1</sup>) as well as a significant pore volume (1.07 cm<sup>3</sup> g<sup>−1</sup>). The initial test with the CSAC electrode, conducted in a 6 M KOH loaded symmetric supercapacitor, demonstrated an ultrahigh capacitance of 367 F g<sup>−1</sup> at a current density of 0.2 A g<sup>−1</sup> together with 92.09% retention after 10,000 cycles at 10 A g<sup>−1</sup>. More impressively, the zinc–ion hybrid supercapacitor using CSAC as a cathode achieves a high-rate capability (153 mAh g<sup>−1</sup> at 0.2 A g<sup>−1</sup> and 75 mAh g<sup>−1</sup> at 10 A g<sup>−1</sup>), high energy density (134.9 Wh kg<sup>−1</sup> at 175 W kg<sup>−1</sup>), as well as exceptional cycling stability (93.81% capacity retention after 10,000 cycles at 10 A g<sup>−1</sup>). Such work thus illuminates a new pathway for converting biowaste-derived carbons into materials for ultrahigh-performance energy storge applications.
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