Electrodeposition of compact silver from ligand-free methanesulfonic acid-based electrolyte containing copper ions

Abstract

Ag coatings have been applied recently as surface finish for electric vehicles. However, conventional electrodeposition uses cyanide in electrodeposition baths, promoting issues on toxicity, environmental and safety concerns, and high cost for wastewater treatment. In this study, a compact Ag film was prepared by electrodeposition in an environmentally-friendly methanesulfonic acid (MSA)-based electrolyte containing Cu²⁺ for application. Electrochemical analyses indicated that the inclusion of Cu²⁺ ions in the electrolyte inhibited Ag⁺ reduction and resulted in grain refinement without alloy formation, particularly during the initial stage of Ag⁺ deposition. The Cu²⁺ ion increased the compactness of the structure, thereby increasing the ultimate tensile strength from 87 MPa to 159 MPa and hardness from 58 Hv_10gf to 67 Hv_10gf, while decreasing the electrical resistivity from 1.77 μΩ∙cm to 1.69 μΩ cm. Additionally, an Ag film with the thickness of 5–6 μm was electrodeposited on busbar-like structure and subjected to a tarnish test in 10 mM Na₂S aqueous solution. The Ag film obtained in a Cu²⁺ -containing bath exhibited better tarnish resistance because of its compactness and small grain size. Therefore, this study demonstrated the fabrication of a compact Ag structure in an acidic ligand-free MSA-based electrolyte with Cu²⁺ ions with potential applications for cases that require an acidic environment, such as pattern plating on a photoresist-covered surface.