Mechanism of the Electrocrystallization of Nickel and Cobalt in Acidic Solution

This mechanism is studied by means of the analysis of the polarization characteristic and of the cathodic impedance. The results, obtained from an acidic solution of the Watts type, strongly support the hypothesis that the cathodic reaction occurs in several steps probably involving an adion . In the case of nickel, the results can be accounted for by a mechanism implying two successive transfer reactions in which acts as an intermediate compound and not as a catalyst. The presence in the electrolyte of either sodium benzenesulfonate or 2‐butyne 1,4‐diol (two inhibitors commonly used for the electrocrystallization of nickel) specifically modifies the kinetic parameters of transfer reactions and diminishes the capacity of the electrochemical double‐layer. This capacity is defined thanks to a least‐squares analysis of the cathodic impedance.