| Summary: | Hierarchically porous activated carbon materials from agro-waste, Jackfruit seeds are prepared by a chemical activation method involving the treatment with zinc chloride (ZnCl<sub>2</sub>) at different temperatures (600–1000 °C). The electrochemical supercapacitance performances of the prepared materials were studied in an aqueous electrolyte (1 M sulfuric acid, H<sub>2</sub>SO<sub>4</sub>) in a three-electrode system. Jackfruit seed carbons display nanoporous structures consisting of both micro- and mesopore architectures and they are amorphous in nature and also contain oxygenated surface functional groups, as confirmed by powder X-ray diffraction (pXRD), Raman scattering, and Fourier-transformed infrared (FTIR) spectroscopy, respectively. The surface areas and pore volumes were found to be 1216.0 to 1340.4 m<sup>2</sup>·g<sup>−1</sup> and 0.804 to 1.144 cm<sup>3</sup>·g<sup>−1</sup>, respectively, demonstrating the better surface textural properties compared to the commercial activated carbons. Due to the high surface area, large pore volume, and well developed hierarchical micro- and mesoporosity, the optimal sample achieved a high specific capacitance of 292.2 F·g<sup>−1</sup> at 5 mV·s<sup>−1</sup> and 261.3 F·g<sup>−1</sup> at 1 A·g<sup>−1</sup> followed by outstanding high rate capability. The electrode sustained 71.6% capacity retention at a high current density of 20 A·g<sup>−1</sup>. Furthermore, the electrode displayed exceptional cycling stability with small capacitance loss (0.6%) even after 10,000 charging–discharging cycles, suggesting that Jackfruit seed would have potential in low-cost and scalable production of nanoporous carbon materials for supercapacitors applications.
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