Cyanide-free silver immersion deposition involving 3-mercapto-1-propanesulfonic acid for copper finishing

Abstract In this work, in the place of cyanide, a novel alternative of silver ligand, 3-mercapto-1-propanesulfonic acid (MPS), is introduced for environmentally friendly copper finishing by a galvanic replacement reaction. The bright yellow and transparent MPS-Ag solution exhibits high chemical and thermal stability. Cyclic Voltammetry (CV) plots prove the coordination ability of MPS to Ag+ is much stronger than that of ammonia in alkaline solution. By applying different temperatures and solution compositions, various silver deposits were prepared by immersion of silver on copper surface in solutions with MPS. The obtained samples were subjected to morphological and chemical characterizations to analyze the composition of corresponding silver deposits. Experimental results show that, the size of the deposited silver particles is tunable by controlling the concentration of Cl− and temperature. Additionally, corrosion tests based on Tafel extrapolation method validate the favorable performance of the corrosion resistance and low coating porosity of the silver deposits. It was observed that, in the absence of Cu+, copper alone cannot reduce the Ag+ in MPS solutions, indicating that Cu+ is the critical component in the reactions involving MPS-assisted replacement. Combined with the experimental output, quantum chemical calculations based on Density Functional Theory (DFT) were employed to explain the mechanism of this particular chemical reaction.