The effect of some primary and secondary brighteners on the double layer capacitance in nickel electrodeposition

Abstract

The capacitance of the double layer at the cathode in a Watts-type nickel-plating solution, containing primary brighteners and secondary brighteners (levelling agents), was measured on a rotating disk electrode using a potential-decay method. Both types of additive increase cathodic polarization and reduce differential capacitance. The effects primary brightenen (p-toluenesulphonamide, saccharin) do not depend on the rate of rotation, wheels those of secondary brighteners (coumarin, thiourea) are more pronounced at greater rotation rates, due to diffusion control of their adsorption on to the cathode during the electrodeposition process.