Highly porous activated carbon from betel palm shells as the prospective electrode for high-performance supercapacitors

Abstract

This research has investigated the viability of valorizing Areca or Betel palm-shells into activated carbon, to be applied as an electrode active material in supercapacitors. The palm-shells are an agricultural waste from betel-nut production, an important economic crop in several regions around the world. The conversion process mainly involves pulverization, ZnCl₂-activation, and carbonization. The effect of carbonization temperatures – 500, 600, 700, and 800 °C, was studied on the properties of the activated carbon. Microstructural characterizations like BET, Raman, and XPS were carried out. All the activated samples are microporous, have a specific surface area >1,000 m² g⁻¹, and possess an intensity ratio of D-to-G band close to 1. More than 80 % of the atomic concentration of the samples is carbon; the C 1s bonds include C=C or sp², C–C or sp³, C–(O,N), C=O, and O–C=O or π– π*. The activated carbon synthesized at 700 °C shows the most favorable properties for being used as the electrode in supercapacitors. Its electrochemical properties, evaluated by galvanostatic charge–discharge and cyclic voltammetry deliver the maximum specific capacitances of 144.48F·g⁻¹ at 1 A·g⁻¹ and 169.21F·g⁻¹ 20 mV·s⁻¹, respectively. The supercapacitors do perform stably at long-term cycling with the capacitance retention (>98 %) and the coulombic efficiency at almost 100 % over 50,000 cycles. The betel-palm-shell carbon has a very comparable capacitive performance to other biomass-derived carbons with the respective maximum energy and powder densities of 7.63 Wh·kg⁻¹ and 5,849.93 W·kg⁻¹. Converting the betel-palm-shell waste, one of the common agricultural wastes in Asia, Oceania, Africa, or Latin America to activated carbon is a pathway of waste valorization as well as leads to a new business opportunity of producing carbon electrodes for an energy application of supercapacitors. This will further go towards a circular carbon economy, not only reducing the carbon footprint and other pollution caused by currently widely practiced incineration, but also creating a sustainable loop of material utilization.