Eco-friendly synthesis of CeO2 nanoparticles using Phyllanthus niruri leaf extract for supercapacitor applications

In this work, Cerium oxide (CeO₂) nanoparticles were successfully prepared via an eco-friendly green route using Phyllanthus niruri leaf extract and evaluated for supercapacitor applications. Unlike conventional chemical synthesis methods, the phytochemical-assisted approach produced high-surface-area CeO₂ nanostructures with enhanced electrochemical activity, enabling their application as efficient supercapacitor electrodes. X-ray diffraction analysis confirmed the formation of a highly crystalline cubic fluorite structure with an average crystallite size of ∼30 nm. Thermogravimetric analysis revealed a total weight loss below 15%, indicating good thermal stability. FTIR spectra confirmed characteristic Ce–O vibrations at 535 and 444 cm⁻¹ along with surface hydroxyl groups. FE-SEM analysis showed agglomerated porous nanostructures, while BET analysis revealed a high specific surface area of 152 m² g⁻¹ and a pore diameter of ∼30 nm, confirming mesoporosity. Electrochemical studies demonstrated combined electric double-layer capacitance and pseudocapacitive behavior due to the reversible Ce³⁺/Ce⁴⁺ redox couple. A high specific capacitance of 496 F g⁻¹ was achieved at 1 A g⁻¹, while cyclic voltammetry showed a maximum capacitance of 478 F g⁻¹ at 10 mV s⁻¹. The electrode exhibited good cycling stability with 84.1% capacitance retention over 5000 cycles. Electrochemical impedance spectroscopy revealed low solution resistance and moderate charge transfer resistance, indicating efficient ion transport and charge transfer kinetics. These results demonstrate that the green synthesized CeO₂ nanoparticles are promising, sustainable promising electrode materials for supercapacitor applications.