Innovative Electrodeposition of Bimetallic Cu–Sn in a Stable Nonelectroactive Pyrophosphate-Based Bath: Reduction and Nucleation Growth Analysis

The timeless allure of Cu–Sn-based intermetallics, commonly known as bronze, stems from their remarkable versatility across a wide range of applications. When used as coatings on stainless steel, Cu–Sn brings forth a host of advantages including enhanced aesthetics, corrosion resistance, low surface tension, weldability, and ductility. However, the electroplating of Cu–Sn onto stainless steel by using acidic baths proves to be a costly affair due to the inherent instability of the acidic solution. Moreover, the short lifespan of the bath necessitates the use of expensive additives. In this study, we present an innovative approach─a stable and cost-effective basic pyrophosphate-based electrolyte bath, to deposit Cu, Sn, and Cu–Sn coatings. Through X-ray diffraction analysis, the Cu–Sn coatings on stainless steel are found to predominantly consist of Cu13.7Sn and Cu3Sn phases, with a minor presence of elemental Sn. Impressively, the Cu–Sn bath exhibits a high current efficiency of 92% and demonstrates exceptional long-term stability, maintaining its integrity for over a year even when exposed to ambient air. To gain deeper insights into the nucleation and growth mechanisms, we conduct a comprehensive investigation employing cyclic voltammetric and chronoamperometric studies. By employing the Scharifker–Hills model, we meticulously analyze the nucleation and growth steps, while further analysis of the cyclic voltammetric results allows us to unravel the intricacies of diffusion kinetics during deposition.