3D flowerlike α-nickel hydroxide with enhanced electrochemical activity synthesized by microwave-assisted hydrothermal method

Nickel hydroxide has received increased attention especially due to its electrochemical properties and potential applications in rechargeable Ni-base alkaline batteries, e.g., Ni/Cd, Ni/Zn, and Ni/MH. Ni(OH)2 has a hexagonal layered structure with two polymorphs, alpha- and beta-Ni(OH)(2). alpha-Ni(OH)(2) shows superior electrochemical properties compared to those of the beta-form. Nanosized flowerlike alpha-nickel hydroxide materials with an interlayer spacing of 7.0 angstrom have been prepared by a microwave-assisted hydrothermal method. The experimental results from XRD and FF-IR showed that the Ni(OH)(2) sample prepared by this method had the typical alpha-phase. FE-SEM images showed many uniform flowerlike architectures with diameters of 700 nm-1 mu m which consisted of the aggregated flakes. TEM results showed the flakes were built up from many nanocrystals with 2-3 nm diameters. TGA and TPD were employed to investigate thermal stability and gas evolution during the heating process. alpha-Nickel hydroxide was transferred to NiO with a cubic crystalline structure after being calcined at 450 degrees C; the NiO still kept the morphology of alpha-Ni(OH)(2). Cyclic voltammetry was used to determine the electrochemical properties of the Ni(OH)(2) electrode in 1 M KOH. alpha-Ni(OH)(2) prepared by MW-HT had the best electrochemical activity for the electrochemical reduction of O-2 compared with alpha-Ni(OH)(2) synthesized by conventional HT methods and beta-Ni(OH)(2). The effects of nickel sources and precipitators on the phase and morphology of the products were studied. Conventional hydrothermal methods were used to study the role of microwave irradiation. The possible growth mechanism is discussed here. The CV experiments showed that H2O2 can be reduced to OH- on the alpha-Ni(OH)(2) electrode. The Levich equation was used to calculate the number of electrons transferred during the O-2 redox reaction.