Redox-Active La ₂ FeNiO ₆ –rGO Nanocomposites as Electrodes with Tuned Electrochemical Properties for Asymmetric Supercapacitor Applications

Hybrid supercapacitors, which integrate electrodes operating through different energy storage mechanisms, have emerged as promising candidates for energy storage devices. In this work, we report in detail the electrochemical evaluation of a La2FeNiO6-reduced graphene oxide (rGO) nanocomposite as an electrode material for a hybrid supercapacitor. Double-perovskite La2FeNiO6 (LFNO) was synthesized via a solvothermal route, and rGO nanosheets were obtained through thermal reduction of graphene oxide at 200 °C. Structural integrity and phase purity were confirmed by X-ray diffraction analysis of both materials. A series of LFNO–rGO nanocomposites (with varying weight ratios) were prepared using a hydrothermal method. Their electrochemical performance was systematically investigated in a 3 M KOH electrolyte using cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy. Among the synthesized composites, the LFNO:rGO composite (LFN1R3) (1:3 weight ratio) exhibited an optimum performance, specific capacitances of ∼1910 F/g at 1 A/g and ∼1391 F/g at 2 A/g, along with rate capability (∼1030 F/g at 1 mV/s), and 87% capacitance retention over 5000 cycles. An assembled asymmetric (LFN1R3//rGO) achieved ∼620 F/g, with a high energy density of 164 Wh/kg and a power density of ∼19 kW/kg, demonstrating its strong potential for next-generation asymmetric supercapacitors.