Electrochemical Synthesis and Characterization of Ni–P Alloy Coatings from Eutectic–Based Ionic Liquid

Ni–P alloy coatings with tunable phosphorus contents are electrodeposited at room temperature using choline chloride:ethylene glycol (1:2 molar ratio) deep eutectic solvent and NiCl 2 ·6H 2 O, NaH 2 PO 2 ·H 2 O as nickel and respectively phosphorous sources. Cyclic voltammetry shows that the presentence of H 2 PO 2 − in the ionic liquid based Ni plating bath promotes the initiation of Ni–P nucleation. Chronoamperometric results indicate that the electrodeposition of Ni and Ni–P alloys on a platinum electrode follows the mechanism of instantaneous nucleation and three-dimensional growth with diffusion-controlled. Surface morphology and chemical composition of the alloy coatings are significantly dependent on the molar ratio of H 2 PO 2 − /Ni 2+ in the electrolyte. Moreover, deposition potential and time have a remarkable effect on the surface morphology of deposits. X-ray diffractometer analysis indicates that the structure of alloys converts from crystalline to amorphous structure as the phosphorus content in the coating increases. Potentiodynamic polarization measurements show that the alloy coating exhibits the nobler corrosion potential and the lower corrosion current density compared with the Ni coating. The more phosphorus content the Ni–P coating has, the more positive corrosion potential and the lower corrosion current density the coating exhibits.