Electrochemical behaviour of nickel anode in H2SO4 solutions and the effect of halide ions

Abstract

AbstractThe electrochemical behaviour of pure nickel in H2SO4 solutions has been potentiodynamically investigated. The effects of the following factors on the anodic dissolution and passivation of the metal are discussed: potential scan rate, successive cyclic voltammetry and progressive additions of Cl−, Br− and I− ions. Increasing the potential scan rate increases the critical current density icc, denoting that the active dissolution of nickel in H2SO4 is a diffusion controlled process. Cyclic voltammetry shows that the reverse excursion does not restore the anode to its active state. On successive cycling, the height of icc decreases; this could be attributed to the decrease in the reduction efficiency of passivating oxide film during the cathodic half cycles.The presence of the halogen ions below a certain concentration specific to each anion inhibits the anodic dissolution both in the active and passive states. The inhibitive action of these additives decreases in the order I−, Br−, Cl−. Beyond the specific concentrations, the halogen ions accelerate the anodic dissolution and shift the active passive transition to more positive values. The aggressiveness of these anions decreases in the sequence Cl−, Br−, I−, Further increase in the halogen ion concentrations can lead to breakdown of the passive film and initiate pitting. The susceptibility of nickel to pitting attack enhances with increasing H2SO4 concentration.