Development of advanced NiO-SiO₂ nanocomposite with flower like morphology, abundant surface oxygen vacancies and enriched Ni²⁺ ions for the efficient oxygen evolution reaction and asymmetric supercapacitor applications

Material morphology, surface area, catalytic site density, and electrical conductivity are pivotal in determining electrocatalytic and electrode properties, directly influencing the efficiency of the oxygen evolution reaction (OER) and the performance of supercapacitors. In this study, a modified hydrothermal method was employed to synthesize in situ NiO-SiO₂ nanocomposites using silica gel and persimmon fruit extract. The synthesis involved varying quantities of silica (1 g and 2 g) and persimmon extract (1 ml and 2 ml), yielding NiO-SiO₂ nanocomposites designated as samples 1 and 2. Sample 1 displayed a porous, flower-like morphology with nanoscale dimensions below 200 nm. Powder X-ray diffraction (PXRD) confirmed the predominance of the cubic NiO phase, while X-ray photoelectron spectroscopy (XPS) identified oxygen defects and a high concentration of Ni²⁺ ions. High-resolution transmission electron microscopy (HRTEM) validated the findings of SEM and XRD analyses. UV–visible spectroscopy revealed a reduced optical band gap for sample 1 compared to other materials. Sample 1 exhibited superior OER activity in 1.0 M KOH, achieving an overpotential of 170 mV at 40 mA cm⁻² with exceptional durability over 40 h. When integrated into an asymmetric supercapacitor (ASC) in 3.0 M KOH, it demonstrated a specific capacitance of 446 F/g at 5 A/g, maintaining 102% capacitance over 40,000 galvanic charge-discharge cycles at 5 A/g. This study highlights a scalable and cost-effective approach to producing NiO-SiO₂ nanocomposites with enhanced electrocatalytic performance and cycling stability, contributing to the advancement of next-generation energy conversion and storage technologies.