High-Capacitance Gold Nanoparticles from <em>Rhus coriaria</em>: Green Synthesis and Electrochemical Evaluation for Supercapacitor Technologies

The structural and electrochemical properties of gold nanoparticles biosynthesized from Rhus coriaria L. (Rc@AuNPs) were comprehensively investigated and characterized. R. co-riaria (sumac) served as a natural gold reducing and capping agent due to its rich poly-phenolic and phytochemical composition, enabling a sustainable, low-cost, and environ-mentally 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 electro-lytes, respectively, indicating strong potential for supercapacitor and energy-storage ap-plications. GCD analysis further showed Csp 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 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 Csp and low ESR observed in KOH demonstrate the excellent capacitive behavior of Rc@AuNPs. These biosynthesized gold nanoparticles represent a promising and sustainable electrode mate-rial for high-performance energy-storage technologies.