High-Capacitance Gold Nanoparticles from Rhus coriaria: Green Synthesis, Characterization and Electrochemical Evaluation for Supercapacitor Technologies

The structural and electrochemical properties of gold nanoparticles biosynthesized from <i>Rhus coriaria</i> L. (Rc@AuNPs) were comprehensively investigated and characterized. <i>R. coriaria</i> (sumac) served as a natural gold reducing and capping agent due to its rich polyphenolic and phytochemical composition, enabling the sustainable, low-cost, and environmentally friendly synthesis of Rc@AuNPs. The electrochemical behavior of the hybrid material was evaluated using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS). Rc@AuNPs exhibited specific capacitances of 129.48 F/g, 156.32 F/g, and 280.37 F/g in H₂SO₄, Na₂SO₄, and KOH electrolytes, respectively, indicating strong potential for supercapacitor and energy-storage applications. GCD analysis further showed <i>C_sp</i> values of 107.69 F/g (H₂SO₄), 133.23 F/g (Na₂SO₄), and 348.34 F/g (KOH), confirming the highest charge-storage performance in basic media. EIS measurements supported these results, yielding equivalent series resistance (ESR) values of 67.96 Ω in H₂SO₄, 64.42 Ω in Na₂SO₄, and a notably lower 24.43 Ω in KOH, consistent with its higher ionic conductivity and more efficient charge transfer. Overall, the superior <i>C_sp</i> and low ESR observed in KOH demonstrate the excellent capacitive behavior of Rc@AuNPs. These biosynthesized gold nanoparticles represent a promising and sustainable electrode material for high-performance energy-storage technologies.