One-pot green bio-assisted synthesis of ZnO/SnO2-rGO hybrid nanocomposites using Prosopis juliflora leaf extract for high-performance supercapacitor electrode

Abstract

The supercapacitor (SC) performance of reduced graphene oxide nanosheets (rGO Ns), ZnO/SnO₂ nanocomposites (ZnO/SnO₂ NCs), and ZnO/SnO₂-rGO hybrid nanocomposites (ZnO/SnO₂-rGO HNCs) was systematically investigated and reported. A one-pot green synthesis method was adopted for the preparation of rGO Ns, ZnO/SnO₂ NCs, and ZnO/SnO₂-rGO HNCs using Prosopis juliflora leaf extract (PJLE) as a green reducing agent. The synthesized samples were analyzed via FTIR, UV, SEM, XRD, DLS, and XPS. Powder XRD confirmed the existence of hexagonal wurtzite-structured ZnO and tetragonal SnO₂ nanoparticles in the ZnO/SnO₂ NCs and ZnO/SnO₂-rGO HNCs. SEM analysis further revealed the successful integration of ZnO nanorods and spherical SnO₂ nanoparticles onto the rGO nanosheet surface. The electrochemical performance of the graphite electrode (GE)-modified ZnO/SnO₂ NCs and ZnO/SnO₂-rGO HNCs was investigated in an acidic electrolyte (1 M H₂SO₄) via cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge discharge (GCD) techniques. The ZnO/SnO₂-rGO HNCs-modified GE demonstrated a greater specific capacitance (SC) of 128.43 F/g in 1 M H₂SO_4, with a capacitance retention of 95.97 % at 1 A/g after 10,000 GCD cycles. Additionally, the constructed symmetric device (ZnO/SnO₂-rGO//ZnO/SnO₂-rGO HNCs) has a high SC of 165.91 F/g, a long-life cycle of 10,000 GCD cycles, and a high energy density (ED) and power density (PD) of 212.36 Wh/kg and 1440 W/kg, respectively, in 1 M H₂SO₄.