Cyclic voltammetric measurements were made on pure copper, nickel and 70/30 copper-nickel alloy in sodium sulphate and sodium chloride (0.5 M) solutions. In sodium sulphate solution the passivation of copper and nickel is through oxide formation. The passive film on copper nickel alloy is found to have nickel ions ingress along with copper oxide by volume diffusion. Nickel ions cause hindrance to the reduction of copper oxide to copper. The presence of chloride ions increases the dissolution of nickel while copper is passivated. The formation of CuCl₂ and its subsequent hydrolysis to hydroxide prevents the dissolution. Introduction of nickel in copper depassivates the copper and hydrolysis of monovalent copper complex is prevented by the ingress of nickel ions. The formation of NiCl₂ along with CuCl₂ is facilitated by chloride ions.

Cupronickels offer enhanced corrosion protection in marine environments by the formation of passive films on the surface. Cyclic voltammetric studies were carried on cupronickels in chloride solutions at pH 6.3 to understand the role of chloride ions in passive film formation. Increase in nickel content of the alloy and of chloride ions in solution decreases film resistance. Chloride ions take part in reduction of the passive film to copper. A solid-state model for passive film formation involving chloride ions has been attempted.