Electrochemical preparation of α-Ni(OH)2 ultrafine nanoparticles for high-performance supercapacitors

Well-dispersed nanoparticles of nickel hydroxide were prepared via a simple electrochemical method. Electrodeposition experiments were performed from 0.005 M Ni(NO3)(2) bath at a constant current density of 0.1 mA cm(-2) on the steel cathode for 1 h. Recording the potential values during the deposition process revealed that the reduction of water has major role in the base electrogeneration at the applied conditions. The obtained deposit was characterized by the X-ray diffraction (XRD), infrared (IR), differential scanning calorimeter-thermogravimetric analysis, carbon-nitrogen-hydrogen (CHN), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. The CHN, XRD, and IR analyses showed that the obtained deposit has alpha phase of Ni(OH)(2) with intercalated nitrate ions in its structure. Morphological characterization by SEM and TEM revealed that the prepared alpha-Ni(OH)(2) is composed of well-dispersed ultrafine particles with the size of about 5 nm. The supercapacitive performance of the prepared nanoparticles was analyzed by means of cyclic voltammetry and galvanostatic charge-discharge tests. The electrochemical measurements showed an excellent supercapacitive behavior of the prepared alpha-Ni(OH)(2) nanoparticles. It was also observed that the alpha-Ni(OH)(2) ultrafine particles have better electrochemical characteristic and supercapacitive behavior than beta-Ni(OH)(2) ultrafine nanoparticles, including less positive charging potential, lower E (a) -aEuro parts per thousand E (c) value, better reversibility, higher E (OER) -aEuro parts per thousand E (a), higher utilization of active material, higher proton diffusion coefficient, greater discharge capacity, and better cyclability. These results make the alpha-Ni(OH)(2) nanoparticles as an excellent candidate for the supercapacitor materials.