Novel tunable hierarchical Ni-Co hydroxide and oxide assembled from two-wheeled units

A novel hierarchical Ni-Co hydroxide assembled from two-wheeled units was successfully synthesized via a simple, hydrothermal method through the reaction of nickel salt, cobalt salt and sodium hydroxide, and with a chelating agent (EDA) to control the precipitation rate. The as-synthesized materials were characterized by x-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FTIR), atomic absorption spectrophotometer (AAS) and thermogravimetric analysis (TG). The Ni2+/Co2+ molar ratio R in the initial solution plays an important role to control the morphology of the hierarchical Ni-Co hydroxide. The influence of the EDA concentration, reaction temperature and NaOH concentration on the formation of the hierarchical Ni-Co hydroxide was also investigated. The formation mechanism of the hierarchical Ni-Co hydroxide assembled by two-wheeled units was proposed. A Ni-Co oxide with a similar structure was obtained by calcination of the as-prepared Ni-Co hydroxide.