Synthesis of activated carbon from perennial wild rice plant (Oryza longistaminata) using Ca(CH3COO)2 activating agent for energy storage supercapacitors.

Abstract

Growing energy demand and the depletion of fossil-based resources have intensified the search for environmentally friendly and renewable electrode materials for energy storage devices. This study reports the production of activated carbon from Oryza longistaminata (perennial wild rice), an abundant aquatic plant with minimal economic value, using calcium acetate obtained from waste eggshells as an activating agent. Activation was conducted at 700 °C, and the material was characterized by Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD) revealing a porous morphology, amorphous carbon structure with partial graphitization, and functional groups. Electrochemical evaluations through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) demonstrated excellent capacitive performance, with the activated carbon delivering a specific capacitance of 258 F g⁻¹ at 0.2 A g⁻¹ in 0.5 M H₂SO₄. The CV curves exhibited a predominantly electric double-layer capacitor (EDCL) behaviour with pseudocapacitance contributions, attributed to surface area, porosity, and oxygen-containing functional groups. The synthesis approach offers dual environmental benefits by valorizing perennial wild rice and recycling eggshell waste, positioning the resultant activated carbon as a promising sustainable electrode material for high-performance supercapacitors.