A method to determine electrochemical kinetic parameters for multi-element anomalous co-deposition of Zn-Ni electroplating

Abstract

Zinc-Nickel alloy plating, an alternative to the carcinogenic cadmium plating was prepared to study the kinetics of reducing elements Zinc, Nickel, and Hydrogen. A methodology to obtain electrochemical kinetic parameters i.e., exchange current density and cathodic transfer coefficient was demonstrated theoretically and experimentally for anomalous co-depositing multielement plating conditions. The kinetic parameters of Zn-Ni plating are very specific to electroplating solution, as the anomalous co-deposition of Zn and Ni either accelerates or retards each other’s deposition behaviour depending on applied potential, which renders standard values or conventional methods such as data optimization ineffective. A continuum-level FEM simulation based on secondary current distribution was performed to predict the plating thickness at a wide range of applied potentials and were found to be in good agreement with experimental results. The deposition behaviour of Zn and Ni align with the hydrogen suppression model, revealing zinc’s significantly higher exchange current density than nickel. The simulation model can effectively predict current density distribution and plating uniformity to explore electroplating of complex geometry in industrial scale while highlighting distinctions in thermodynamic and practical nobility of Zn and Ni for optimum plating composition.