Effects of Bromide Ions in Anomalous Codeposition of Ni-Co Alloys with a Sulfamate Based Electrolyte

Alloy electrodeposition of Ni-Co alloys is known to show an anomalous codeposition behavior, which the concentration of cobalt in the deposited alloy is higher than the concentration of cobalt ions in the electrolyte. In this study, the cobalt content in the alloy is increased from 30 at% to 60 at% through introduction of bromide ions into a sulfamate bath, while addition of chloride ions does not give any significant influences to the alloy. The bromide ions are found to promote the reduction of cobalt ions but inhibit the reduction of nickel ions. Effects of the pH are also investigated to provide possible explanation to the phenomenon observed, and the anomalous codeposition behavior becomes more obvious in a more acidic electrolyte.