The NiO nanocrystals were successfully prepared by calcinating Ni(OH)(2) precursor synthesized via a facile ion diffusion controlled by ion exchange membrane without adding any solvent or template. Xray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) isotherm, X-ray photoelectron spectroscopy (XPS) and Ultraviolet-visible (UV-vis) analysis were used to investigate the crystallinity, morphology, surface and porosity characteristics, chemical composition and optical properties in more detail. The pseudocapacitive behavior of the NiO samples was investigated by cyclic voltammograms (CV) and galvanostatic charge-discharge tests in 2 M KOH. The results analysis reveals that both specific capacitance and surface area decrease with the increase of calcination temperatures. Among the NiO samples, the NiO-400 nanoflakes calcinated at 400 degrees C possess the highest specific capacitance of 381 Fg(-1) at a current density of 2 A g(-1), but much lower than the Ni(OH)(2) sample. In addition, the UV-vis analysis shows that there is a red shift of absorption peak for the three NiO samples with the increasing temperature and the NiO-400 has a broad band gap of 3.3 eV, which renders the material highly interesting for application in photocatalyst. (C) 2016 Elsevier B.V. All rights reserved.