Electrodeposition mechanism and characterization of Ni–Cu alloy coatings from a eutectic-based ionic liquid

The electrodeposition mechanism, microstructures and corrosion resistances of Ni–Cu alloy coatings on Cu substrate were investigated in a choline chloride–urea (1:2 molar ratio) eutectic-based ionic liquid (1:2 ChCl–urea IL) containing nickel and copper chlorides. Cyclic voltammetry showed that the onset reduction potentials for Cu (∼−0.32 V) and for Ni (∼−0.47 V) were close to each other, indicating that Ni–Cu co-deposition could be easily achieved in the absence of complexing agent which was indispensable in aqueous plating electrolyte. Chronoamperometric investigations revealed that Ni–Cu deposits followed the three-dimensional instantaneous nucleation/growth mechanism, thus producing a solid solution. The compositions, microstructures and corrosion resistances of Ni–Cu alloy coatings were significantly dependent on the deposition current densities. Ni–Cu alloy coatings were α-Ni(Cu) solid solutions, and the coating containing ∼17.6 at.% Cu exhibited the best corrosion resistance because of its dense and crack-free structure.