Grapefruit juice containing rich hydroxyl and oxygenated groups capable of transforming 1D structure of NiCo2O4 into 0D with excessive surface vacancies for promising energy conversion and storage applications

Abstract

Fabrication of an efficient electrode material is highly demanded for obtaining high energy conversion electrochemical system. In this study, we describe a green and innovative approach of using grape fruit juice as a high carrier of reducing and surface modifying agents for manipulating the surface properties of nickel‑cobalt bimetallic oxide NiCo2O4 nanostructures. Different amounts of grape fruit juice were used to discern its role on the morphological and surface vacancies of NiCo2O4 nanostructures during oxygen evolution reaction (OER). Importantly, the physical characterization revealed the morphological transformation of NiCo2O4 nanostructures from 1D nanorods to short range 0D nanoparticles. Furthermore, the surface studies have shown that NiCo2O4 nanostructures prepared with grapefruit juice have high density of surface vacancies and higher amount of Ni2+ and a Co2+ metallic ions on the surface of NiCo2O4 compare to pure NiCo2O4 nanostructures. The OER of electrodes modified with NiCo2O4 nanostructures, particularly (sample-2, 2 mL of grape fruit juice) gave rise to an overpotential value of 260 mV at 10 mAcm−2 in 1.0 M KOH aqueous solution along with high durability/stability for 40 h. Additionally, the obtained electrochemical impedance spectroscopy value of 80 Ω and active surface area of 18.1 μFcm−2 attested for the excellent OER performance of NiCo2O4 nanostructures (sample-2). Eventually, the proven enhancement in surface vacancies, alternation in the mixed oxidation states of both Ni and Co together with the morphological transformation that have been accomplished via the green, simple, and low-cost strategy of using grape juice make it a suitable option for large scale production of wide range of multifunctional metal oxides and related nanostructured materials for plethora of energy conversion and storage applications.