Void-Free Smooth Nickel Electrodeposition with Supercritical Carbon Dioxide Emulsified Sulfamate Bath in High Current Density

Supercritical carbon dioxide (scCO 2 ) emulsions are used in the electrodeposition of nickel from a nickel sulfamate bath at current densities ranging from 0.03 to 0.36 A cm −2 . ScCO 2 emulsions are formed by mixing scCO 2 , surfactants, and the aqueous nickel sulfamate bath. Nickel films obtained by electrodeposition with scCO 2 emulsions (ESCE) were compared to those produced by conventional electrodeposition (CONV). The use of scCO 2 emulsions improves the quality of the nickel film, even at high current densities up to 0.36 A cm −2 , as evidenced by reduced grain size and decreased surface roughness. The Faradaic efficiency (FE) of the deposition reaction by CONV gradually decreased from 95% to 90% as the current density increased from 0.03 to 0.36 A cm −2 , while the FE by ESCE decreased from 82% to 70%. The lowered FE is suggested to result from promoted hydrogen evolution due to the introduction of scCO 2 emulsions. Grain refinement and an increased Vickers hardness value of up to 780 HV are attributed to the periodic plating characteristic mechanism.