Green Synthesis and RSM Optimization of Endostemon viscosus-derived α-MoO₃ Nanostructures for Supercapacitor Applications

Abstract

This study introduces a sustainable plant-mediated strategy for preparing electrochemically active α-MoO₃ nanostructures using Endostemon viscosus leaf extract and evaluates their potential as supercapacitor electrode materials. The aqueous leaf extract was prepared from 10 g of dried leaves in 100 mL of distilled water at 80 °C for 30 min, followed by its reaction with ammonium heptamolybdate precursor solution and subsequent aging, washing, drying, and calcination. XRD confirmed well-crystallized orthorhombic α-MoO₃ with an average crystallite size of approximately 28 nm, while TGA indicated satisfactory thermal stability with 91.4% residual mass. FTIR confirmed characteristic Mo=O and Mo–O–Mo vibrations, and FE-SEM revealed agglomerated flake-/sheet-like nanostructures with interconnected porous regions. EDS showed 66.66 wt.% Mo and 33.34 wt.% O, while BET analysis yielded a specific surface area of approximately 118 m² g⁻¹ and an average pore diameter of 18 nm. Electrochemical measurements demonstrated a maximum specific capacitance of approximately 458 F g⁻¹ at 5 mV s⁻¹ from CV and 360 F g⁻¹ at 0.5 A g⁻¹ from GCD. The electrode retained 94.3% of its initial capacitance after 5000 cycles and exhibited low series and charge-transfer resistances of approximately 1.8 and 7.2 Ω, respectively. Overall, the developed α-MoO₃ nanostructures exhibited promising electrochemical performance for supercapacitor applications. Future studies should focus on developing complete two-electrode devices and evaluating energy density, power density, long-term cycling stability, and practical operating performance.