Sonochemical intercalation synthesis of nano γ-nickel oxyhydroxide: Structure and electrochemical properties

Nano γ-nickel oxyhydroxide (nano γ-NiOOH), intended as a new positive electrode material for alkaline Zn/Ni batteries, was synthesized by a sonochemical intercalation method. Using NaClO as oxidant, 5 M NiCl2 solution was added dropwise to a concentrated alkaline solution of NaClO + NaOH, which allows all four elementary reactions (precipitation, oxidation, cation exchange, and water molecule intercalation) to proceed simultaneously under low-frequency ultrasonic irradiation. XRD, SAXS, TEM, SEM, AAS, IR, TG, CT (complexometric titration), cyclic voltammetry (CV), and a charge–discharge test of imitative cell have been used to characterize the microstructural characteristics, composition and electrochemical properties of the synthesized material. The results showed that the lattice parameters of nano γ-NiOOH are a = 2.8256 Å and c = 20.7938 Å. The average oxidation state of Ni in the sample is 3.65 as measured by an indirect iodine method. The alkali metallic Na+ ions and water molecules have been inserted into sites between NiO2 layers. The cyclic voltammogram of nano γ-NiOOH exhibited two cathodic peaks and two anodic peaks, which is in accord with the redox reaction between the various phases of Ni(OH)2 and NiOOH. The charge–discharge test of imitative cells revealed that nano γ-NiOOH exhibited a higher discharge capacity than spherical β-NiOOH.