The kinetics of nickel electrodeposition

By means of impedance measurements, the kinetics of nickel electrocrystallization has been further investigated in strongly acidified chloride electrolytes and in electrolytes containing two additives: 2 butyne 1,4 diol (2B 1,4D) and sodium benzenesulfonate (BS). In chloride solutions at pH 0.5, besides the two inductive effects previously mentioned for less acidified solutions, a capacitive low-frequency feature has been pointed out. The addition of 2B 1,4D has an inhibiting effect more pronounced in chloride than in sulfate solutions. In chloride electrolytes the inductive low-frequency effect is observed up to potentials more negative than in additive-free electrolytes. With the addition of BS in Watts or in chloride electrolytes, both an inductive and a capacitive low-frequency feature appear. A reaction mechanism is proposed, accounting for the specific effects of the anions. In sulfate electrolytes it involves the interaction between adsorbed hydrogen strongly bonded to the surface and the intermediate adions Niads(1). In chloride electrolytes the model is based on the slow desorption of an adsorbed anionic species. This reaction mechanism also accounts for the effects of 2B 1,4D and BS additions on the electrode kinetics.