Microwave-assisted gas/liquid interfacial synthesis of flowerlike NiO hollow nanosphere precursors and their application as supercapacitor electrodes

A rapid method based on an efficient gas/liquid interfacial microwave-assisted process has been developed to synthesize flowerlike NiO hollow nanosphere precursors, which were then transformed to NiO by simple calcinations. The wall of the sphere is composed of twisted NiO nanosheets that intercalated with each other. Such hollow structure is different from widely reported flowerlike nanostructures with solid cores. An Ostwald ripening mechanism was proposed for the formation of the hollow nanostructures. The products were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution TEM, energy-dispersive X-ray analysis, and N₂ adsorption-desorption methods. These flowerlike NiO hollow nanospheres have high surface area of 176 m² g^-1. Electrochemical properties show a high specific capacitance of 585 F g^-1 at a discharge current of 5 A g^-1 and excellent cycling stability, suggesting its promising potentials in supercapacitors.