Potential Oscillations During Cobalt–Nickel Electrodeposition in the Presence of Butynediol

Electrochemical potential oscillation is observed during the electrodeposition of CoNi in the presence of butynediol (BD). Modulation of the potential oscillatory pattern occurs due to the influence of differing proton and BD concentrations through diffusion/convective diffusion on the surface processes. The potential oscillation observed is a relaxation type as a result of the interplay between (a) hydrogen adsorption by proton reduction and the scavenging of adsorbed hydrogen by BD and (b) CoNi hydroxide precipitation by water reduction and the dissolution of CoNi hydroxide by protons. Moreover, the precipitation of CoNi hydroxide occurs at a lower current density while the BD concentration is high, whereas the absence of BD necessitates a higher current density for observing the precipitation. This result suggests that BD plays a critical role in altering the interfacial pH during CoNi electrodeposition