In this work, mesoporous NiO with three-dimensional flowerlike morphology were synthesized from precursor alpha-Ni(OH)(2) by a facile template-free modified homogeneous precipitation method, where CO (NH2)(2) could be acted as a chelating agent at lower temperatures, and source material of OH-utilizing the hydrolysis reaction at high temperatures. The structures of the NiO materials were characterized by X-ray diffraction, Fourier transform infrared spectroscopy and transmission electron microscopy. The specific surface area of NiO was 140 m(2) g(-1), which was about 86% of the specific surface of precursor alpha-Ni(OH)(2) (163 m(2) g(-1)). The pore diameter of NiO and alpha-Ni(OH)(2) were approximately 3.6 nm and 1.7 nm, corresponding to mesoporous and microporous, respectively. The NiO material used as an electrode in 6 mol L-1 KOH electrolyte exhibited a specific capacitance of 289 F g(-1) at a current density of 5 A g(-1), and could still retain 262 F g(-1) at 10 A g(-1) and 257 F g(-1) at 20 A g(-1), respectively. In addition, almost no decrease of the capacitance was observed after 4000th charge-discharge cycles at a current density of 10 A g(-1). (C) 2015 Elsevier Ltd. All rights reserved.