Preparation and characterization of self-assembled layer by layer NiCo2O4–reduced graphene oxide nanocomposite with improved electrocatalytic properties

Abstract

NiCo2O4 nanoparticles dispersed on reduced graphene oxide (RGO) are prepared by simultaneously reducing graphene oxide (GO), nickel and cobalt nitrate via a hydrothermal method assisted by post annealing at low temperature. The method involves formation of hydroxides on GO using ammonia under hydrothermal conditions. Subsequent thermal treatment at 300°C led to the conversion of hydroxides into single-phase NiCo2O4 atop the RGO. The synthesized products are characterized through several techniques including X-ray diffraction (XRD), ultraviolet–visible spectroscopy (UV–Vis), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy (RS), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The FE-SEM investigations reveal the growth of a layer by layer assembly of NiCo2O4–RGO (2:1) nanocomposite, where the NiCo2O4 nanoparticles are tightly packed between the layers of RGO. Further, the catalytic properties of the NiCo2O4–RGO nanocomposite are investigated for the oxygen evolution reaction (OER) through cyclic voltammetry (CV) measurements. It is observed that the special structural features of the NiCo2O4–RGO (2:1) nanocomposite, including layer by layer assembly, integrity and excellent dispersion of the NiCo2O4 nanoparticles atop the RGO, produced a synergistic effect and therefore significantly improved the electrochemical performance. The oxidation potential (0.135V) of NiCo2O4–RGO (2:1) nanocomposite was observed to be lower than that of bare NiCo2O4 nanoparticles (0.33V), whereas the corresponding current densities were measured to be 4.1mA/cm2 and 3.11mA/cm2, respectively.