Sequestration of Activated Carbon from a Wasteland Weed and its Application in High Performance Supercapacitor-based Energy-Storage System

Abstract

The urge to satisfy the growing energy demands in the present scenario, the world is exploring novel renewable sources, producing various energy forms as well as searching alternative to non-renewable sources. The plants and raw organic matters are otherwise known as biomass, used to explore in several segments like biofuels, biochars and energy storage applications. Supercapacitors, otherwise known as electrical double layer capacitors (EDLCs), are storage devices with advantages of high-power density, long cycle life, safe operation and shelf life. The above mentions make EDLCs, a promising candidate for next generation energy storage device. It is a well-established fact that activated carbon is manifested as an important adsorbent to be used in numerous applications over the years. The carbonaceous material with small and low volume pores leads to activated carbon, with excellent adsorbent media owing to high surface area, free valencies, porous attribute, surface reactivity and good adsorption capacity. The synthesis of various forms of activated carbon has been investigated frequently by numerous researchers using several chemical agents. The current experiment is envisaged upon highly porous carbon with ZnCl2 and ZnCl2-ethanol activation. The planning of experiment is optimized with a suitable statistical method i.e., Taguchi orthogonal array, to get appropriate data along with improved field performance, reliability and low cost. The optimum factors affecting entire synthesis process and surface properties are determined with Taguchi L9 orthogonal array and ANOVA (analysis of variance) technique. The present study speaks of the synthesis of wild sugarcane or Saccharum spontaneum, as the prime sample, which is processed in to porous carbon. The raw material is found abruptly in the riverside, possessing nearly no use to the mankind, thus considered as a wasteland weed. The chemical treatment of the samples is performed with ZnCl2 as a major activating agent. The ZnCl2 and ZnCl2-ethanol activated carbons are synthesized with distinctive impregnation ratio (1-3) and carbonization temperature (500 ℃ - 800 ℃). The samples are characterized to observe the surface properties in terms of functionalities, morphologies, surface area and porosity. The best-found sample with optimum results is further tested in electrochemical storage system for EDLC application. The sample synthesized with ZnCl2-ethanol activation, at 600 ℃ shows optimum performance in terms of surface area (1590 m2/g) and porous properties. The same is reflected in the sample for energy storage performance. In an aqueous 1M H2SO4 electrolyte, the specific capacitance of 561 F/g and 275 F/g is achieved in half-cell and full-cell studies, respectively. The enhancement in electrochemical properties is clear with addition of redox additives. Herein, the incorporation of 0.01M hydroquinone, a redox agent, results raise in specific capacity up to 1392 C/g (half-cell) and 658 C/g (full-cell). Similarly, remarkable cycle stability of 77% after 5000 cycles, in HQ-incorporated aqueous electrolyte is obtained, evidencing high performance of EDLC device. A parallel trend is followed in energy density, power density and other relevant electrochemical properties as well.