High-surface area and large porosity carbon materials with hierarchically porous structures are the preferred electrode materials for high-energy density supercapacitors. In this contribution, we report the preparation of ultrahigh surface area nanoporous carbon materials with hierarchically micro- and mesopore structures from Artocarpus heterophyllus (Jackfruit) seed. This involves a potassium hydroxide (KOH) activation method conducted at higher temperatures (600–1000 °C). The resulting amorphous carbon materials display outstanding performance as electrodes in electrical double-layer capacitors with an aqueous electrolyte (1 M H2SO4), which is due to their partially graphitic structures, ultrahigh surface areas of ca. 2104.3 m2 g–1, and large pore volumes of ca. 1.386 cm3 g–1. Electrodes prepared from the material with optimal textural parameters lead to a high specific capacitance of 323.8 F g–1 at 1 A g–1 and sustained 53.7% capacitance retention at a high current density of 50 A g–1, demonstrating the high rate performance of the electrode. The experimental results suggested fast diffusion of the electrolyte ions near the surface of the electrode, which was verified using molecular simulations. The simulations verified that the electrolyte enters the pores, thereby increasing the capacitance but reducing the charge rate compared to nonporous electrodes. Additionally, an exceptionally long cycle stability was observed with 97% of the capacitance retained after 10,000 charge–discharge cycles. The results show the considerable probability of Jackfruit-seed-derived hierarchically porous carbons as the electrode materials for high-performance supercapacitor applications.

Hierarchical porous carbon materials with high surface area and large porosity derived from biomass are desired for the sustainable development of low-cost electrode materials for advanced energy storage devices. Here, we report the electrochemical supercapacitance performance of washnut seed-derived nanoporous carbon materials in aqueous electrolyte (1 M H2SO4) on a three-electrode system. Potassium hydroxide (KOH) activation of the pre-carbonized Washnut seed powder at high temperatures (800–1000 °C) under nitrogen atmosphere yielded nanoporous carbons with hierarchical micro- and mesoporous structure with well-developed porosity. The surface areas and pore volumes are found in the range of 2005 to 2185 m2 g−1 and 1.370 to 2.002 cm3 g−1, respectively. The as-prepared materials showed outstanding electrochemical energy storage performance achieving a high specific capacitance of 288.7 F g−1 at a current density of 1 A g−1 followed by a high rate capability sustaining 67.2% capacitance even at a high current density of 50 A g−1 with only a small capacity loss (<2%) after 10,000 charging/discharging cycles. This work demonstrates novel insights into low-cost high-performance carbon materials design using natural biomass for the sustainable development of electrode materials for advanced supercapacitor applications.

Hierarchically porous activated carbon materials from agro-waste, Jackfruit seeds are prepared by a chemical activation method involving the treatment with zinc chloride (ZnCl2) at different temperatures (600–1000 °C). The electrochemical supercapacitance performances of the prepared materials were studied in an aqueous electrolyte (1 M sulfuric acid, H2SO4) 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 m2·g−1 and 0.804 to 1.144 cm3·g−1, 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−1 at 5 mV·s−1 and 261.3 F·g−1 at 1 A·g−1 followed by outstanding high rate capability. The electrode sustained 71.6% capacity retention at a high current density of 20 A·g−1. 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.

Biomass-derived activated carbon materials with hierarchically nanoporous structures containing nitrogen functionalities show excellent electrochemical performances and are explored extensively in energy storage and conversion applications. Here, we report the electrochemical supercapacitance performances of the nitrogen-doped activated carbon materials with an ultrahigh surface area prepared by the potassium hydroxide (KOH) activation of the Nelumbo nucifera (Lotus) seed in an aqueous electrolyte solution (1 M sulfuric acid: H2SO4) in a three-electrode cell. The specific surface areas and pore volumes of Lotus-seed–derived carbon materials carbonized at a different temperatures, from 600 to 1000 °C, are found in the range of 1059.6 to 2489.6 m2 g−1 and 0.819 to 2.384 cm3 g−1, respectively. The carbons are amorphous materials with a partial graphitic structure with a maximum of 3.28 atom% nitrogen content and possess hierarchically micro- and mesoporous structures. The supercapacitor electrode prepared from the best sample showed excellent electrical double-layer capacitor performance, and the electrode achieved a high specific capacitance of ca. 379.2 F g−1 at 1 A g−1 current density. Additionally, the electrode shows a high rate performance, sustaining 65.9% capacitance retention at a high current density of 50 A g−1, followed by an extraordinary long cycle life without any capacitance loss after 10,000 subsequent charging/discharging cycles. The electrochemical results demonstrate that Nelumbo nucifera seed–derived hierarchically porous carbon with nitrogen functionality would have a significant probability as an electrical double-layer capacitor electrode material for the high-performance supercapacitor applications.

Of the available environmentally friendly energy storage devices, supercapacitors are the most promising because of their high energy density, ultra-fast charging-discharging rate, outstanding cycle life, cost-effectiveness, and safety. In this work, nanoporous carbon materials were prepared by applying zinc chloride activation of lotus seed powder from 600 °C to 1000 °C and the electrochemical energy storage (supercapacitance) of the resulting materials in aqueous electrolyte (1M H2SO4) are reported. Lotus seed-derived activated carbon materials display hierarchically porous structures comprised of micropore and mesopore architectures, and exhibited excellent supercapacitance performances. The specific surface areas and pore volumes were found in the ranges 1103.0–1316.7 m2 g−1 and 0.741–0.887 cm3 g−1, respectively. The specific capacitance of the optimum sample was ca. 317.5 F g−1 at 5 mV s−1 and 272.9 F g−1 at 1 A g−1 accompanied by high capacitance retention of 70.49% at a high potential sweep rate of 500 mV s−1. The electrode also showed good rate capability of 52.1% upon increasing current density from 1 to 50 A g−1 with exceptional cyclic stability of 99.2% after 10,000 cycles demonstrating the excellent prospects for agricultural waste stuffs, such as lotus seed, in the production of the high performance porous carbon materials required for supercapacitor applications.