Nickel deposition from unbuffered neutral chloride solutions in the presence of oxygen

A comparison is made between depositions from neutral unbuffered chloride solutions of nickel with and without the presence of oxygen. In the presence of oxygen, a poorly conductive layer of Ni(OH) 2 is formed early because of oxygen reduction which occurs prior to nickel deposition. The surface Ni(OH) 2 inhibits the first charge transfer reaction of Ni 2+ to active intermediate (categorically represented by Ni(OH) ads, and subsequently diminishes the nucleation and growth of nickel. The effect is more pronounced in region with little hydrogen evolution. Surface flakes characteristic of uninhibited nickel deposition are clearly absent in the scanning electron micrographs of deposits. The current efficiency of nickel deposition is slightly increased in the presence of oxygen. It is also found that the oxygen effect is more effective in 0.1 M NiCl 2. This is due to the fact that uninhibited deposition of nickel and hydrogen evolution, which are promoted by high and low Ni 2+ concentration respectively, are less efficient than oxygen effect at an intermediate concentration level.