Abstract
A simple process is reported of the large-scale synthesis of microspherical mixed phase alpha-and beta-Ni (OH)(2) nanofibers produced by precipitation from aqueous NiCl2-NH4OH. These microspheres, with diameters of 20-50 mu m, are composed of three-dimensional, nanoporous nanofibers, oriented along the radial direction. The nanofibers have lengths of 300-1000 nm, diameters of 30-50 nm and a specific surface area of 286.4 m(2) g(-1). The effects of temperature and concentration on the morphology of the products were studied systematically, and the nanofiber growth mechanism was investigated. It was found that the nanostructure of Ni(OH)(2) could be changed from microspheres to nanoflakes, to nanofibers and nanoparticles, as the NiCl2 concentration is increased from 2 to 8 M, and for NH4OH concentrations from 10 to 14 M. The as-synthesized nanofibers exhibit excellent charge-discharge performance and the highest yet capacitance of 1271 F g(-1) for electrochemical supercapacitors, which is much higher than beta-Ni(OH)(2) nanoplates (797 F g(-1)) and commercial Ni(OH)(2) powder (529.4 F g(-1)) at 1 A g(-1) current density. The results indicate that as-synthesized hierarchical nanofibers, composed of mixed a-and beta-Ni(OH)(2) phases, are an excellent candidate for energy storage applications. The large-scale commercialization of our laboratory-produced nanofibers is also discussed.