Cathodic Deposition of Zinc-Nickel Coatings from a Dilute Ammonium Chloride Electrolyte with a High Glycine Concentration

Abstract

This study determined the kinetics of the synthesis, the chemical composition, and morphology of zinc-nickel coatings electrolytically obtained from low-concentration (0.04 М ZnCl2, 0.08 M NiCl2) ammiacate and ammonia-glycinate chloride solutions. Transient electrochemical methods (cyclic voltammetry and linear sweep voltammetry) allowed us to determine that the cathodic deposition of Zn–Ni alloy costings, regardless of the presence of glycine in the ammonium chloride electrolyte, is limited by the stage of diffusion mass-transfer of ions, whose electrochemical reduction (the charge transfer stage) is irreversible. The introduction of relatively high concentrations of glycine (0.3 М) in the electrolyte allows obtaining smoother coatings, which is demonstrated by the results of scanning electron microscopy. At the same time, energy dispersive X-ray spectroscopy demonstrated that the atomic fraction of nickel in the potentiostatically deposited coating increases on average by 9.7%. It is possible that the alteration of the chemical composition results in a significant decrease (on average by ~15 %) in the current efficiency in electrolytes with glycine, since it catalyses the side reaction of hydrogen evolution.

Keywords

• electrodeposition
• zinc-nickel coatings
• ammine electrolyte
• glycine
• current efficiency
• voltammetry.