Role of Mo6+ during nickel electrodeposition from sulfate solutions

Abstract

The effect of Mo6+ on the current efficiency, deposit quality, surface morphology, crystallographic orientations and polarisation behaviour of the cathode during electrodeposition of nickel from sulfate solutions was investigated. Mo6+ did not have a significant effect on current efficiency over the concentration range 2–100 mg dm−3. However; a decrease in current efficiency by a magnitude of more than 20% was seen at 500 mg dm−3. The quality of the nickel deposit with reference to the visual appearance and contamination level varied with varying concentration of Mo6+; this was also reflected in the morphology and crystallographic orientations of the deposits. Addition of Mo6+ to the electrolyte introduced two new crystal planes i.e., (220) and (311). Depolarisation of the cathode was noted at lower concentrations of Mo6+ (2–40 mg dm−3) whereas polarisation of the cathode was observed at Mo6+ concentration >40 mg dm−3 .The effect of Mo6+ on parameters such as Tafel slope (b), transfer coefficient (α) and exchange current density (i 0) were also determined.