Utilization of guarana (Paullinia cupana) biowaste from the Amazon for supercapacitor electrode production

Abstract The valorization of Amazonian biomass residues into porous carbon materials represents a sustainable strategy for the development of energy storage technologies. In this study, guarana ( Paullinia cupana ) husk, an agro-industrial by-product, was converted into activated carbon through pyrolysis followed by KOH chemical activation for supercapacitor electrode investigations. The resulting PG-ATK5 carbon exhibited a significant structural evolution after activation, with its BET specific surface area increasing from 7.06 to 600.35 m 2 g − 1 , accompanied by the formation of a predominantly microporous network with an average pore size of approximately 1.2 nm. Structural and surface analyses revealed a disordered carbon framework, evidenced by XRD and Raman spectroscopy, with an increase in the I D /I G ratio from 1.02 to 1.35, indicating the generation of defects and edge sites suitable for ion adsorption. Electrochemical evaluation in a three-electrode configuration demonstrated typical electric double-layer capacitor behavior, with symmetrical galvanostatic charge–discharge profiles and a characteristic frequency response indicating charge propagation. The PG-ATK5 electrode exhibited a specific capacitance of 101.02 F g − 1 at 1 A g − 1 and retained approximately 52% of its capacitance at 7 A g − 1 . This behavior indicates moderate rate capability, constrained by ion transport within the narrow microporous structure. Overall, these results indicate the potential of guarana husk as a renewable and low-cost precursor for the preparation of porous carbons, supporting its use as a sustainable feedstock for electrode materials in electrochemical energy storage investigations.