Effect of Cd 2þ on the electrodeposition of nickel from sulfate solutions. Part II: Polarisation behaviour U.S. Mohanty a , B.C. Tripathy a , P. Singh b, * , S.C. Das a a Department of Hydrometallurgy, Regional Research Laboratory (CSIR), Bhubaneswar 751013, India b Department of Chemistry, South Street, Murdoch University, Murdoch, WA 6150, Australia Received 11 February 2003; received in revised form 31 October 2003; accepted 10 November 2003 Abstract The effect of Cd 2þ on the electrodeposition of nickel from a sulphate bath in the absence and presence of boric acid has been investigated. The presence of Cd 2þ ion suppresses the nickel electrodeposition and shifts the deposition potential to more negative values. The cathodic polarisation is found to depend on the composition of the electrolytic bath. For the various baths investigated, the cathodic polarization order is found to decrease in the order NiSO 4 +H 3 BO 3 > NiSO 4 +H 3 BO 3 + Na 2 SO 4 > NiSO 4 + Na 2 SO 4 > NiSO 4 . For the Ni 2þ electroreduction reaction on stainless steel and nickel substrates the exchange current density de- creases with increase in Cd 2þ concentration in the electrolytic bath. However the Tafel slope and transfer coefficient are unaffected. Ó 2003 Elsevier B.V. All rights reserved. Keywords: Electrodeposition; Nickel; Cadmium; Sodium sulphate; Boric acid; Kinetic parameters 1. Introduction The electrodeposition of nickel has been studied by several investigators with respect to current efficiency, polarisation behaviour and deposit structural charac- teristics [1–10]. Likewise the effects of several common cationic and anionic impurities during electrodeposition of nickel are also well documented in the literature [11– 23]. The nickel electrodeposition from baths, especially the bright plating baths, are very sensitive to impurities such as Mg 2þ , Cu 2þ , Zn 2þ , Cr 3þ and sulphur containing organic compounds [20]. These impurities, besides in- creasing the tendency of pitting, also change the char- acteristics of the electrodeposited metal. Budniok et al. [24] studied the effect of Cd 2þ on the electrocrystallisa- tion of copper from an ethylene diamine electrolyte. They found that cadmium polarised the electrode and blocked the single crystal copper substrate due to un- derpotential adsorption. Watson and Walters [25] re- ported that addition of chromium particles to a Watts type electrolyte shifted the nickel electroreduction wave to more positive potentials on a vitreous carbon surface. Gogia and Das [26] studied the polarisation behav- iour of nickel in the presence of cationic impurities such as Co 2þ , Cu 2þ , Fe 2þ , Fe 3þ by linear sweep voltammetry. They found that while Fe 2þ polarised the cathode, Fe 3þ depolarised it. Similarly they found that while depolar- isation of the electrode occurred at lower concentrations of Co 2þ , polarisation occurred at higher concentrations of Co 2þ . However in the case of Cu 2þ they found that there was no shift in the cathode potential. Zhou et al. [27] studied the polarisation behaviour of nickel in the presence of Al 3þ and Cr 3þ and found that addition of both Al 3þ and Cr 3þ polarised the cathode. Since Cd 2þ is one of the major impurities in the electrolytic baths from which nickel is electrowon com- mercially, we are carrying out a systematic study of the effect of this ion on the characteristics of nickel elec- trodeposition. In our previous paper [28] we reported that the presence of Cd 2þ in the nickel electrolyte affects the CE, crystal orientations and deposit morphology of nickel electrodeposited on a stainless steel cathode from acidic sulphate baths. In a continuation of our previous * Corresponding author. Tel.: +61-8-9360-2379; fax: +61-8-9310- 1711. E-mail address: singh@chem.murdoch.edu.au (P. Singh). 0022-0728/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jelechem.2003.11.010 Journal of Electroanalytical Chemistry 566 (2004) 47–52 www.elsevier.com/locate/jelechem Journal of Electroanalytical Chemistry