Electrochemical investigation of Ni-P autocatalytic deposition in ammoniacal solutions

The kinetics of Ni-P autocatalytic deposition in ammoniacal solutions was investigated by means of cyclic voltammetry and electrochemical impedance spectroscopy. The effect of the solution constituents (hypophosphite, nickel salt and pH) was examined. Strong interactions between the cathodic and anodic processes occur. The metal discharge is enhanced by the oxidation of hypophosphite, which is the predominant reaction in this process. The nickel deposition also affects the anodic process. With increasing pH the nickel discharge is progressively inhibited due to the change in the nature of the Ni(II) complexes. In contrast, in the presence of Ni(II) species, due to the opposite effect of the two partial processes, the plating rate increases for pH values up to 9 and then decreases for higher pH values.