Deciphering rGO-Driven Interfacial Modulation: Bridging Frequency−Voltage-Dependent Electrical Characteristics and Electrochemical Performance in NiO/ZnO Composites

Abstract

The rising energy demand and exhaustion of fossil fuel resources have expedited the search for efficient and sustainable energy storage technologies. This study presents the hydrothermal synthesis of NiO/ZnO (NZ) binary nanocomposite and its ternary nanocomposites with 4 wt % (NZR1) and 8 wt % (NZR2) reduced graphene oxide (rGO) for supercapacitor applications. The structural, morphological, vibrational, and chemical characteristics were analyzed using powder X-ray diffraction (PXRD), field emission-scanning electron microscopy (FE-SEM), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The electrochemical performance was evaluated using cyclic voltammetry (CV), galvanostatic charge−discharge (GCD), and electrochemical impedance spectroscopy (EIS) in a 2 M Na2SO4 electrolyte, while frequency- and voltage-dependent electrical measurements were employed to elucidate the charge-transport dynamics. Of the electrodes prepared, NZR2 exhibited the optimal performance, with a specific capacitance of 785 Fg−1 at 1 Ag−1, minimal solution resistance, and 81.7% capacitance retention after 5000 cycles. Electrical investigations revealed the frequency dependence of dielectric relaxation and alternating current conduction. The characteristic relaxation frequency of 1.438 MHz and a relaxation time of 110.69 ns were determined for NZR2. A notable enhancement in conductivity at 5 V was reported, indicating field-assisted charge transport, alongside suppressed diffusion-limited processes and reduced resistance. The aggregated findings demonstrate that the enhanced performance of NZR2 stems from the synergistic interaction of ZnO-driven electrical transport, NiO-facilitated pseudocapacitive activity, and rGO-enabled electronic connectivity and electric double-layer capacitance. The correlation between electrochemical performance and electrical transport and relaxation dynamics substantiates NZR2 as an appropriate electrode material for sustainable energy storage applications.