Kinetics of electrodeposition of nickel from watts baths

Tafel slopes and reaction orders for the electrodeposition of nickel from Watts type baths onto a vitreous carbon electrode have been determined by both steady state and transient methods. After correcting the currents for concurrent hydrogen evolution, and taking the composition of the deposit into account, the following kinetic parameters have been obtained: Tafel slope 120 mV decade−1, reaction orders with respect to nickel and chloride both +1. The agreement between the two methods was excellent. No dependence of cathodic rate constants on pH could be found. The cathodic results do not therefore support the widely held opinion that an adsorbed complex involving a hydroxide ion is an intermediate in active dissolution. Results for the nucleation constant are given in the Appendix. The nucleation constant for nickel on vitreous carbon is found to depend on potential and concentration of nickel ions, and to be independent of pH and concentration of chloride ions.