Abstract
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.