Preparation and characterization of self-assembled layer by layer NiCo ₂O₄-reduced graphene oxide nanocomposite with improved electrocatalytic properties

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 NiCo₂O ₄-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 NiCo₂O ₄ nanoparticles atop the RGO, produced a synergistic effect and therefore significantly improved the electrochemical performance. The oxidation potential (0.135 V) of NiCo₂O₄-RGO (2:1) nanocomposite was observed to be lower than that of bare NiCo₂O₄ nanoparticles (0.33 V), whereas the corresponding current densities were measured to be 4.1 mA/cm² and 3.11 mA/cm², respectively.