In this work, we demonstrate the influence of nickel oxides with divergent particle sizes as the working electrodes for supercapacitor application. The nanostructured nickel oxide (NiO) is synthesized via facile sonochemical method, followed by calcination process. The crystallinity and surface purity of prepared samples are clearly examined by X-ray diffraction and Raman analysis. NiO crystallinity is significantly increased with increasing calcination temperatures. The surface analysis confirmed that the calcination at 250 degrees C exhibited nanoclutser like NiO with average particle size of similar to 6 nm. While increasing the calcination temperature beyond 250 degrees C, hexagonal shaped NiO is observed with enhanced particle sizes. The electrochemical performance confirmed the good redox behavior of NiO electrodes. Moreover, NiO with average particle size of 6 nm exhibited high specific capacitance of 449 Fig at a scan rate of 5 mV/s compared to other samples with particle sizes of similar to 21 nm (323 F/g) and similar to 41 nm (63 F/g). This is due to the good ion transfer mechanism and effective electrochemical utilization of the working electrode. (C) 2016 Elsevier Inc. All rights reserved.