Abstract:
Electrochemical capacitors- known as supercapacitors- have attracted phenomenal attention in energy sector as sustainable and affordable energy storage systems for their advantageous characteristics over batteries and conventional capacitors. Herein, we have demonstrated a chemical route for the modification of rGO-MnO2 by Ni and Fe3O4 nanoparticles for the synthesis of porous and hollow crumpled (--)@rGO-MnO2, core-shell Ni@rGO-MnO2, core-shell Fe3O4@rGO-MnO2 nanocomposite with a very high electrochemical capacitance as compared to MnO2 on flat reduced graphene sheet (rGO-MnO2). Core-shell Ni@rGO-MnO2, Fe3O4@rGO-MnO2 nanocomposites were successfully synthesized through the in-situ chemical redox reaction between KMnO4 and benzyl alcohol on Ni@rGO and Fe3O4@rGO, respectively. Porous and hollow crumpled (--)@rGO-MnO2 was obtained from core-shell Ni@rGO-MnO2, Fe3O4@rGO-MnO2 by chemical etching of Ni and Fe3O4 from Ni@rGO and Fe3O4@rGO core separately using HCl. The chemical analysis, morphology and structure were demonstrated using FTIR, EDX, FESEM, and XRD, respectively. The electrochemical energy storage performance was evaluated in a three-electrode system in 0.5 M Na2SO4 solution through cyclic voltammetry (CV) and galvanostatic charge-discharge techniques (GCD) within -0.1 to 0.8 V for Ni-based nanoparticles and -0.15 to 0.75 V for iron oxide-based nanocomposite and electrochemical impedance spectroscopy (EIS) of synthesized nanocomposites were studied. Core-shell Ni@rGO-MnO2 and hollow and porous (--)@rGO-MnO2 nanocomposite exhibited an enhanced specific capacitance (Csp) of 327 F/g and 688 F/g respectively, whereas that for rGO-MnO2 was only 189 F/g at 0.1 A/g current density within potential range -0.1 to 0.8 V . Core-shell Fe3O4@rGO-MnO2 and hollow crumple (--)@rGO-MnO2 nanocomposite showed Csp 625 F/g and 1086 F/g respectively, whereas that for rGO-MnO2 was only 252 F/g at 0.1 A/g current density within potential range -0.15 to 0.75 V. As (--)@rGO-MnO2 exhibited low charge transfer resistance as compared to rGO-MnO2, with extended double-layer capacitance, which is due to the combination of hollow and porous crumpled reduced graphene and embedded needle and rod-like nanostructure of manganese dioxide, are responsible for high specific capacitance with good performance in cycle stability for each case and presented the highly promising application for supercapacitors.
KEYWORDS: Supercapacitor, reduced graphene oxide, manganese oxide, core-shell nanocomposite.
