Shape-selective synthesis of NiO nanostructures for hydrazine oxidation as a nonenzymatic amperometric sensor

In this work, we demonstrate the shape-dependent electrocatalytic activity of NiO NPs towards hydrazine oxidation. For this purpose, NiO NPs, having pellet, rod, dot and cuboid-shapes, were synthesized using a variety of reducing agents such as sodium hydroxide (NaOH) with polyethylene glycol (PEG), NaOH without PEG, ammonia (NH₃), and sodium carbonate (Na₂CO₃) via a simple and low cost sol-gel approach. Moreover, NiO-silica core-shell (NiO@SiO₂) NPs were prepared using TEOS as a source of the porous silica. The morphological structures of these NPs were characterized by field emission-scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). From the X-ray diffraction (XRD) results, a face-centered cubic (fcc) NiO crystalline structure was confirmed and the estimated size of the crystalline NPs was in the range of 2.7-12.5 nm depending on the reducing agents utilized for the synthesis. Moreover, their characteristics were further investigated by Raman spectroscopy. From the cyclic voltammetry results, it was shown that the nano-pellet shape NiO exhibited the best electrocatalytic performance for hydrazine oxidation and stability, promising for fuel cell application.