Aqueous synthesis and growth of morphologically controllable, hierarchical Ni(OH)(2) nanostructures

We report a simple route for the synthesis of several morphologies of self-assembling hierarchical Ni (OH)2 nanostructures, by the reaction of NiSO4 and NH4OH in aqueous solution, at a constant temperature, using neither surfactant nor template. Both morphology and microstructure depend on the concentrations of the reactants, the reaction temperature and the anions (Cl-, .., NO3- and SO42-) present. The nanostructures have been characterized by scanning electron microscopy (SEM) and x-ray diffraction (XRD). When SO42-is used, irrespective of the presence of other anions, only microspheres of hierarchical Ni(OH)2 nanosheets are present, suggesting that this anion plays a critical role in microsphere formation. Electrochemical characterizations of Ni(OH)2 nanosheets show good supercapacitor performance, with relatively high capacity and excellent rate capability, indicating that these hierarchical Ni(OH)2 nanosheets are serious candidates for energy storage applications. The growth mechanism for nanosheet formation is discussed, based on SEM observations under different preparation conditions, detailing the transition from nanoparticles to nanowires to nanosheets. The specific surface area and the thickness of our Ni(OH)2 nanosheets have been determined to be 149.6 m2 g-1 and 20-30 nm, respectively.