Analysis of Co-Pd alloys deposition from electrolytes based on [Co(NH3)6]3+ and [Pd(NH3)4]2+ complexes

This work comprises results of the studies on the mechanism and kinetics of hexaamminecobalt(III) and tetraamminepalladium(II) co-reduction in ammonia-chloride solutions at pH 9.5. Electrolyte stability was determined by UV-Vis absorbance measurements. Electrochemical investigations were performed by applying cyclic voltammetry (CV) combined with electrochemical quartz crystal microbalance (EQCM) as well as with spectrophotometric measurements. The results indicated that the reduction process of [Co(NH3)6]3+ consists of two steps. In the first step [Co(NH3)6]3+ is reduced to [Co(NH3)4]2+ and [Co(NH3)5]2+, and then ammonia complexes of Co2+ are reduced to Co0. The M/z values determined during electrogravimetric measurements indicate that the reduction process of [Pd(NH3)4]2+ takes place in one step due to 2-electrons irreversible reduction reaction. Deposition of Co and Pd take place only in the overpotential deposition range. It was found that the examined reactions are diffusion-controlled. In anodic part M/z values and registered CV's indicate cobalt(II) hydroxide oxidation.