Green synthesis of biomass-derived graphene for supercapacitor application

This study investigates the structural evolution of graphene oxide (GO), hydrothermally carbonized graphene oxide (HTC), and reduced graphene oxide (rGO), focusing on the effects of hydrothermal treatment durations (48 h and 72 h) on the electrochemical performance. GO samples exhibit crumpled, layered morphologies with wrinkled flakes due to oxygen functionalization, while thermal reduction to rGO results in restacked sheets and a more compact texture, indicating partial restoration of sp² domains. These structural changes enhance surface area, promote ion diffusion, and suggest improved suitability of the materials for supercapacitor electrode applications. Prolonged hydrothermal treatment increased functionalization, and subsequent thermal reduction in rGO samples selectively removed some oxygen groups, preserving redox-active sites and supporting improved electron transport. Cyclic voltammetry and galvanostatic charge-discharge analyses revealed that rGO@48 exhibited the highest specific capacitance (552.48 F g^-1 at 1 A g^-1) and best rate performance, attributed to its partially restored sp² carbon structure and preserved porosity. Electrochemical impedance spectroscopy confirmed low charge transfer resistance and favorable capacitive behavior for rGO@48, while rGO@72 showed the poorest performance due to restacking and limited ion diffusion. These findings indicate that a 48 h hydrothermal carbonisation followed by controlled reduction yields promising electrochemical properties for supercapacitor electrode application.