Effect of EDTA and NH4Cl additives on electrodeposition of Zn-Ni films from choline chloride-based ionic liquid

Two additives of ethylene diamine tetraacetic acid (EDTA) and ammonium chloride (NH4Cl) were separately used in the electrodeposition of Zn-Ni alloy films from a deep eutectic solvent. The effects of these two additives on electrodeposition behavior, composition, morphology, and corrosion performance of the Zn-Ni alloys were investigated. The electrodeposition behaviors of Zn-Ni alloy revealed by the cyclic voltammetry show that the addition of EDTA to the Zn-Ni electrolyte enhances the Zn incorporation into the alloy film while the addition of NH4Cl produces an opposite effect by suppressing Zn incorporation into the film. With an increase of EDTA concentration in the electrolyte, the Zn content of the Zn-Ni films increases, while the grain size of the deposits and the current efficiency of the plating process decrease. The increase of NH4Cl concentration in the electrolyte would significantly refine the grain size of the electrodeposited Zn-Ni films, reduce the Zn content and increase the cathodic current efficiency. The corrosion testing indicates that the barrier corrosion resistances of Zn-Ni films electrodeposited from NH4Cl containing electrolytes are superior to those electrodeposited from EDTA-containing electrolytes, which in turn are superior to those electrodeposited from additive-free electrolytes.