Butynediol’s Role beyond Brightening Additive during Electrodeposition of Cobalt

Abstract

Butynediol (2-Butyne-1,4-diol), a well-known type-II brightening additive, changes the interfacial p H resulting in the formation of porous cobalt hydroxide film of ca. 1 μ m thickness over the copper substrate in a short duration of electrodeposition (2 min) and at a very low current density (−5 mA cm −2 ) from sulfate bath. In the absence of butynediol, a metallic cobalt layer was observed under identical deposition conditions. The choice of anions (sulfates, chlorides and nitrates) in the electrodeposition bath determines the kind of electrodeposited films obtained, viz ., cobalt, cobalt/cobalt hydroxide, and compact cobalt hydroxide. The adsorption of butynediol enhances hydrogen evolution due to water reduction that facilitates the formation of porous microstructures of cobalt hydroxide. Competition for adsorption sites between butynediol and chloride and dissolution of cobalt hydroxide by diffusing protons result in a mixed metallic cobalt particle and porous cobalt hydroxide microstructure. The variations in the phases and microstructures of electrodeposits were evidenced through the difference in the magnetic and electrocatalytic properties.