Passivation of Nickel in NaOH Solutions

The passivation behavior of Ni electrode in NaOH solutions is studied by cyclic voltammetry technique. Different experimental factors, such as, electrolyte concentration, voltage scanning rate and the sweeping potential range are examined. The cyclic voltammgrams data, Cvs, indicated a correlation between two well-defined anodic oxidation peaks and only cathodic peak. The first anodic peak was attributed to the oxidation of Ni to Ni(OH)(2), followed by a passive region corresponding to the transformation of Ni(OH)(2) to -NiOOH. The second anodic peak was suggested to correspond to the oxidation of Ni(OH)(2) or NiO to some higher oxides of nickel. The cathodic branch of the cyclic voltammogram was characterized by only one cathodic peak, which was splitted into two sub peaks on increasing the concentration of NaOH. These peaks are thought to correspond to the reduction of (or part of) the products formed during the second anodic peak.