A study of the preparation of NiOx electrode via electrochemical route for supercapacitor applications and their charge storage mechanism

NiOx thin film electrodes were prepared for use in a supercapacitor by electrochemical precipitation of Ni(OH)(2) films followed by heat-treatment. The effect of electrodeposition conditions such as cathodic current density and concentration of Ni(NO3)(2) solution on the surface morphology of NiOx were examined and found to have a significant effect on the surface morphology of the deposited films. The surface morphology of the NiOx films changed from dense to porous morphology with an increase in the deposition rate of Ni(OH)(2) films. A maximum specific capacitance of 277 F/g was obtained for a highly porous NiOx film electrode prepared by heating the Ni(OH)(2) film deposited at 4.0 mA/cm(2) in 0.1 M Ni(NO3)(2) at 300degreesC. The charge-storage mechanism of NiOx in 1 M KOH was investigated using an electrochemical quartz crystal microbalance (EQCM) and probe beam deflection (PBD) technique. Nonmonotonic mass change was observed during redox reactions of the nickel oxide film in 1 M KOH. Analysis of the EQCM and PBD results showed that the electrochemical redox reaction of the NiOx is not a simple OH- adsorption/desorption reaction but rather composed of predominant H+ desorption in the initial stage of oxidation and thereafter predominant OH- adsorption in the latter stage of oxidation and vice versa during reduction. (C) 2001 The Electrochemical Society.